Awk, sed and grep, commonly known as the three Musketeers under Linux, have many similarities between them, but they also have their own characteristics. The similarity is that they can all match texts, among which sed and awk can also be used for text editing. , and grep does not have this function. Sed is a non-interactive and character-oriented stream editor (a "non-interactive" stream-oriented editor), and awk is a pattern-matching programming language because its main function is to match text and Processing, at the same time, it has some programming language syntax, such as functions, branch loops, variables, etc. Of course, compared to our common programming language, Awk is relatively simple.
Using Awk, we can do the following things:
Think of a text file as a text database consisting of fields and records;
Variables can be used in the operation of the text database;
Ability to use mathematical operations and string manipulation
Ability to use common programming structures such as conditional branching and looping;
Can format the output;
Ability to customize functions;
Ability to execute UNIX commands in awk scripts;
Ability to handle the output of UNIX commands
With the above functions, awk can do a lot of things. But the journey of a thousand miles begins with a single step. We start with the most basic command line syntax and step into the awk programming world.
Command line syntax
Like sed, awk's command line syntax has two forms:
Awk [-F ERE] [-v assignment] ... program [argument ...] awk [-F ERE] -f progfile ... [-v assignment] ...[argument ...]
The program here is similar to the script in sed, because we have always emphasized that awk is a programming language, so the awk script is treated as a piece of code. The awk script can also be written to a file and specified with the -f parameter, which is the same as sed. Program generally consists of multiple pattern and action sequences. When the read record matches the pattern, the corresponding action command is executed. One thing to note here is that in the first form, except for the command line options, the program parameter must be in the first position.
Awk's input is parsed into multiple records. By default, the record's delimiter is, so one line can be considered as a record, and the record's delimiter can be changed by the built-in variable RS. When the record matches a pattern, the subsequent action command is executed.
Each record is further divided into multiple fields. By default, the field separators are whitespaces, such as spaces, tabs, and so on. They can also be changed by the -F ERE option or the built-in variable FS. In awk, you can access the corresponding field by $1, $2..., and $0 to store the entire record, which is similar to the command line position parameter in the shell. We will explain these contents in detail below. You just need to know these things.
The standard awk command line parameters are mainly composed of the following three:
-F ERE: defines the field delimiter, the value of this option can be extended regular expression (ERE);
-f progfile: Specifies the awk script. Multiple scripts can be specified at the same time. They are connected in the order in which they appear on the command line.
-v assignment: Defines the awk variable, in the same form as the awk variable assignment, ie name=value, and the assignment occurs before the awk handles the text;
For ease of understanding, here are a few simple examples. Set the colon with the -F parameter: as a delimiter, and print each field:
[kodango@devops ~]$ echo "1:2:3" | awk -F: '{print $1 " and " $2 " and " $3}'1 and 2 and 3
Access the variables set with the -v option in the awk script:
[kodango@devops ~]$ echo | awk -va=1 'BEGIN {print a}'1
As you can see from the above, the variables set with the -v option are accessible at the BEGIN location. BEGIN is a special pattern that will be executed before awk handles input. It can be thought of as an initialization statement, and END is also corresponding to this.
It seems that we haven't introduced how to specify the files to be processed. Isn't the final argument the specified file? Before I read this book, I also think so, but in fact there are two forms of arguemnt, they are the input file (file) and variable assignment (assignment).
Awk can specify multiple input files at the same time. If the file name of the input file is '-', it means that the content is read from the standard input.
The variable assignment is similar to the -v option, which takes the form name=value. The variable name in awk is not much different from the general programming language, but it can't be the same as the awk reserved keyword. You can check the awk manual to find out which keywords are reserved. The variable value has only two forms: string and value. Variable assignments must be placed after the parameters of the script, and there is no order of precedence for the file name parameters, but the timing of the assignment of the variable at a different location is different.
We use actual examples to explain this difference. Suppose there are two files: a and b. Their contents are as follows:
[kodango@devops awk_temp]$ cat afile a[kodango@devops awk_temp]$ cat bfile b
To illustrate the timing of the assignment operation, we print the value of the variable in three places: BEGIN, normal processing, and END.
The first case: The variable assignment precedes all file name parameters
[kodango@devops awk_temp]$ awk 'BEGIN {print "BEGIN: " var} {print "PROCESS: " var} \END {print "END: " var }' var=1 aBEGIN: PROCESS: 1END: 1
Result: The assignment operation occurs before normal processing, after the BEGIN action.
The second case: variable assignment is located after all file names:
[kodango@devops awk_temp]$ awk 'BEGIN {print "BEGIN: " var} {print "PROCESS: " var} \END {print "END: " var }' a var=1 BEGIN: PROCESS: END: 1
Result: The assignment operation occurs after normal processing, before the END action.
The third case: variable assignments are between file names:
[kodango@devops awk_temp]$ awk 'BEGIN {print "BEGIN: " var} {print "PROCESS: " var} \END {print "END: " var }' a var=1 bBEGIN: PROCESS: PROCESS: 1END: 1
Result: The assignment operation occurs after the previous file is processed and before the file following the processing;
Summarized as follows:
If the variable is assigned before the first file parameter, it is executed after the BEGIN action, affecting normal processing and END action.
If the variable is assigned after the last file parameter and before the END action, it only affects the END action.
If the file parameter does not exist, the situation is the same as described in 1;
If the variable assignment is between multiple file parameters, the file in front of the variable assignment is processed after execution, affecting subsequent file processing and END actions;
Therefore, the assignment of variables must be considered for clarity, otherwise it is more prone to errors, but in most cases, variable assignment will not be used.
Naturally, you would compare the variable assignment with the -v assignment option. The form of the assignment is the same, but the timing of the -v option is earlier than the variable assignment:
[kodango@devops awk_temp]$ echo 1 | awk -v var=a 'BEGIN {print "BEGIN: " var}'BEGIN: a
It can be seen that the assignment of the -v option is performed before the BEGIN action.
The variable assignment must be careful not to repeat the name with the reserved keyword, otherwise it will give an error:
[kodango@devops awk_temp]$ echo 1 | awk -v BEGIN=1 'BEGIN {print "BEGIN: " BEGIN}'awk: fatal: cannot use gawk builtin `BEGIN' as variable name
Record and Field
For a database, a database table is composed of multiple records, each row represents a record. Each record consists of multiple columns, each column showing a field. Awk treats a text file as a text database, so it also has the concept of records and fields. By default, the separator for the record is a carriage return, and the separator for the field is a whitespace character, so each line of the text file represents one record, and the contents of each line are separated into multiple fields by blanks. Using fields and records, awk can handle the contents of a file with great flexibility.
The default field delimiter can be modified with the -F option. For example, each line of /etc/passwd is separated by colons into multiple fields, so here you need to set the delimiter to a colon:
[kodango@devops awk_temp]$ awk -F: '{print $1}' /etc/passwd | head -3rootbindaemon
Here the first person field is referenced by $1, similarly $2 represents the second field, $3 represents the third field.... $0 indicates the entire record. The built-in variable NF records the number of fields, so $NF represents the last field:
[kodango@devops awk_temp]$ awk -F: '{print $NF}' /etc/passwd | head -3/bin/bash/bin/false/bin/false
Of course, $(NF-1) represents the penultimate one.
The built-in variable FS can also be used to change the field separator, which records the current field separator:
[kodango@devops awk_temp]$ awk -F: '{print FS}' /etc/passwd | head -1:[kodango@devops awk_temp]$ awk -v FS=: '{print $1}' /etc/passwd | Head -1root
Recorded separators can be changed by the built-in variable RS:
[kodango@devops awk_temp]$ awk -v RS=: '{print $0}' /etc/passwd | head -1root
If you set RS to empty, the behavior is a bit weird. It treats all rows (one paragraph) that are not consecutive blank lines as one record and forces the carriage return to the field delimiter:
[kodango@devops awk_temp]$ cat awk_man.txt The awk utility shall execute programs written in the awk programming language,which is specialized for textual data manipulation. An awk program is a sequence of patterns and corresponding actions. When input is read that matches apattern , the action associated with that pattern is carried out.Input shall be interpreted as a sequence of records. By default, a record is a line,less its terminating
Here, we assign the variable assignment to the BEGIN action, because the BEGIN action is executed before the file processing and is used specifically for the initialization statement. The assignment of FS is invalid here, and awk still uses carriage returns to separate fields.
Script composition
The program section in the command line can be called awk code, or awk script. An awk script consists of multiple 'pattern {action}' sequences. The action is one or more statements that are executed when the input line matches the pattern. If pattern is empty, this action will be executed on every line. The following example simply prints each line of the file, where the print statement without any parameters prints the entire record, similar to 'print $0':
[kodango@devops awk_temp]$ echo -e 'line1line2' | awk '{print}' line1line2
In addition to pattern {action}, you can also define custom functions in the script. The function definition format is as follows:
Function name(parameter list) { statements }
The function's parameter list is separated by commas. The parameters are local variables by default and cannot be accessed outside the function. The variables defined in the function are global variables and can be accessed outside the function, such as:
[kodango@devops awk_temp]$ echo line1 | awk 'function t(a) { b=a; print a;} { print b; t("kodango.me"); print b;}'kodango.mekodango.me
The statements in the Awk script are separated by blank lines or semicolons, and the semicolon can be placed on the same line, but sometimes it affects readability, especially in branching or looping structures. It is easy to make mistakes.
If a statement in Awk is too long to be split into multiple lines, you can use a backslash '\' in the behavior:
[kodango@devops awk_temp]$ cat test.awk function t(a){ b=a print "This is a very long line, so use backslash to escape the newline hen we will print the variable a: a=" a} { Print b; t("kodango.me"); print b;}[kodango@devops awk_temp]$ echo 1 | awk -f test.awk This is a very long line, so use backslash to escape the newline then we will print The variable a: a=kodango.mekodango.me
Here we write the script to a file and specify it with the -f parameter. However, after some special symbols, it is possible to directly wrap, such as ", {&& ||".
Pattern
The pattern is a more important part of awk, it has the following situations:
/regular expression/: Extended Regular Expression. About ERE, please refer to this article;
Relational expression: A relational expression, such as greater than, less than, or equal to, a relational expression that results in a true match;
BEGIN: A special pattern that is executed before the first record is processed and is often used to initialize the statement's execution;
END: A special mode that is executed before the last record is processed and is often used to output summary information;
Pattern, pattern: pattern pairs, matching all records between the two, similar to sed address pairs;
For example, find the line that matches the number 3:
[kodango@devops awk_temp]$ seq 1 20 | awk '/3/ {print}'313
Conversely, you can add a '!' before the regular expression to indicate a mismatch:
[kodango@devops awk_temp]$ seq 1 5 | awk '!/3/ {print}'1245
In addition to the two special modes BEGIN and END, the rest of the modes can be combined using the '&&' or '||' operators. The former represents logical AND and the latter represents logical OR:
[kodango@devops awk_temp]$ seq 1 50 | awk '/3/ && /1/ {print}'1331
The preceding regular lines are all full line matches, sometimes only need to match a certain character, so we can use the expression $n ~ /ere/:
[kodango@devops ~]$ awk '$1 ~ /ko/ {print}' /etc/passwdkodango:x:1000:1000::/home/kodango:/bin/bash
Sometimes we just want to display specific and lines, such as displaying the first line:
[kodango@devops ~]$ seq 1 5 | awk 'NR==1 {print}'1
Regular Expression
Like sed, I won't go into detail here about regular expressions. Because the content of the regular expression is too complicated to introduce, it is still recommended that students read the existing articles (such as the POSIX specification of Linux/Unix tools and regular expressions), and the regular expressions of each genre are summarized clearly.
Expressions
Expressions can consist of constants, variables, operators, and functions. The values ​​of constants and variables can be strings and numbers.
There are three types of variables in Awk: user-defined variables, built-in variables, and field variables. Among them, the built-in variable names are all capitalized.
Variables are not necessarily declared or initialized. The default value of a variable is an empty string, which is implicitly automatically converted to a number 0 (eg, a mathematical operation) in some contexts. Remember that the variable in awk is No type, there is no difference between a string variable or a numeric variable, but sometimes it is said to be easy to understand. (Thanks for the reminder from Netizen @ Ziyun Ye)
Field variables can be referenced using $n, where n is in the range [0, NF]. n can be a variable, such as the last field of the $NF code, and $(NF-1) represents the penultimate field.
An array
An array is a special kind of variable. The arrays in awk are all associative arrays, and their subscripts are all string values ​​(manual in the manual is: All arrays in AWK are associative, ie indexed by string values), even though The subscript you use is a number, and awk implicitly converts the subscript into a string. So it is easy to misunderstand that the subscript of an array can be a number or a string.
The assignment of the array is very simple. The following assigns value to the element indexed by the array:
Array[index]=value
You can iterate over array elements using the syntax for..in.. where item is the index of the array element:
For (item in array)
Of course you can also use the in operator in the if branch decision:
If (item in array)
A complete example is as follows:
[kodango@devops ~]$ echo "1 2 3" | awk '{for (i=0;i Built-in variables Awk internally maintains a number of built-in variables, or system variables, such as FS, RS, and so on. Common built-in variables are shown in the following table variable name description The following introduces a few more difficult to understand built-in variables: 1. ARGV and ARGC The meaning of ARGV and ARGC is better understood, just like the C language main (int argc, char **argv). The index of the ARGV array starts at 0 and goes to ARGC-1. It stores the command line parameters and excludes the command line options (such as -v/-f) and the program section. Therefore, in fact, ARGV is just the storage part of the argument, the file name (file) and the command line variable assignment of the two parts. Here are some examples of how ARGC and ARGV can be used: [kodango@devops awk_temp]$ awk 'BEGIN {> for (i = 0; i < ARGC; i++)> print ARGV[i]> }' inventory-shipped BBS-listawkinventory-shippedBBS-list The usage of ARGV is not limited to this. It can be modified. You can change the value of an array element, add an array element, or delete an array element. a. Change the value of ARGV element Suppose we have a, b two files, each with a line content: file a and file b. Now using ARGV, we can do it: [kodango@devops awk_temp]$ awk 'BEGIN{ARGV[1]="b"} {print}' afile b It should be noted here that the quotes for ARGV[1]="b" cannot be missing, otherwise ARGV[1]=b assigns the value of the variable b to ARGV[1]. When awk finishes processing a file, it will get the parameters from the next element of ARGV. If it is a file, it will continue processing. If it is a variable assignment, it will perform the assignment operation: [kodango@devops awk_temp]$ awk 'BEGIN{ARGV[1]="var=1"} {print var}' a b1 Why is the variable value printed only once? You can go back and look at the contents of the variable assignment in the previous article. When the next element is empty, it skips no processing so that you can avoid processing a file: [kodango@devops awk_temp]$ awk 'BEGIN{ARGV[1]=""} {print}' a bfile b In the above example, a file was skipped. When the value of the next element is "-", it means that the content is read from standard input: [kodango@devops awk_temp]$ awk 'BEGIN{ARGV[1]="-"} {print}' a baa # --> Press CTRL+D here to stop inputting file b b. Remove the ARGV element The effect of removing an ARGV element and assigning the element's value to null is the same, and they both jump to the processing of a parameter: [kodango@devops awk_temp]$ awk 'BEGIN{delete ARGV[1]} {print}' a bfile b Delete array elements can use the delete statement. c. Increase the ARGV element The first time I saw the ARGV variable, I wondered if I could use the ARGV variable to avoid providing command-line arguments, like so: Awk 'BEGIN{ARGV[1]="a";} {print}' But in fact this does not work, awk will still get content from standard input. The following method is possible, first increase the ARGC value, and then increase the ARGV element, and I have not understood the difference between the two: [kodango@devops awk_temp]$ awk 'BEGIN{ARGC+=1;ARGV[1]="a"} {print}'file a 2. CONVFMT and OFMT Awk allows numeric-to-string conversions, where the built-in variable CONVFMT defines the format of the awk internal value-to-string conversion. Its default value is "%.6g": [kodango@devops awk_temp]$ awk 'BEGIN { printf "CONVFMT=%s, num=%f, str=%s", CONVFMT, 12.11, 12.11}' CONVFMT=%.6g, num=12.110000, str=12.11 By changing CONVFMT, we can define our own conversion format: [kodango@devops awk_temp]$ awk 'BEGIN { CONVFMT="%d"; printf "CONVFMT=%s, num=%f, str=%s", CONVFMT, 12.11, 12.11 }' CONVFMT=%d, num= 12.110000, str=12 Correspondingly, there is also a built-in variable OFMT, which is similar to CONVFMT in that it only affects the format of numbers converted to strings when affecting the output: [kodango@devops awk_temp]$ awk 'BEGIN { OFMT="%d";print 12.11 }' 12 3. ENVIRON ENVIRON is an associative array of system environment variables. Its subscript is the environment variable name, and the value is the value of the corresponding environment variable. E.g: [kodango@devops awk_temp]$ awk 'BEGIN { print ENVIRON["USER"] }' kodango You can also pass values ​​to awk using environment variables: [kodango@devops awk_temp]$ U=hello awk 'BEGIN { print ENVIRON["U"] }' hello You can use the for..in loop to iterate through the ENVIRON array: [kodango@devops awk_temp]$ awk 'BEGIN { for (env in ENVIRON) printf "%s=%s", env, ENVIRON[env]; }' 4. RLENGTH and RSTART Both RLENGTH and RSTART are related to the match function. The former indicates the length of the matched substring, and the latter indicates that the matched substring is located at the start index of the target string. E.g: [kodango@devops ~]$ awk 'BEGIN {match("hello,world", /llo/); print RSTART,RLENGTH}'3 3 About the match function, we will introduce later. Operator Operators are inevitably necessary in expressions. The operators supported by awk can be found in the "Expressions in awk" section of the man page: [kodango@devops awk_temp]$ man awk | grep "^ *Table: Expressions in" -A 42 | sed 's/^ *//' Table: Expressions in Decreasing Precedence in awkSyntax Name Type of Result Associativity( expr ) Grouping Type Of expr N/A$expr Field reference String N/A++ lvalue Pre-increment Numeric N/A--lvalue Pre-decrement Numeric N/Alvalue ++ Post-increment Numeric N/Alvalue -- Post-decrement Numeric N/Aexpr ^ Expr Exponentiation Numeric Right! expr Logical not Numeric N/A+ expr Unary plus Numeric N/A- expr Unary minus Numeric N/Aexpr * expr Multiplication Numeric Left... omitted below... Statement So far, the more used statement is print, and the others are printf, delete, break, continue, exit, next, and so on. The difference between these statements and functions is that they don't use parenthesized arguments and they don't have a return value. However, there are also accidents. For example, printf can be called like a function: [kodango@devops awk_temp]$ echo 1 | awk '{printf("%s", "abc")}'abc The break and continue statements should be understood by everyone. They are used to jump out of the loop and jump to the next loop. Delete is used to delete an element in an array, which we used when we introduced ARGV above. The use of exit, as its name implies, is to exit awk processing and then execute the contents of the END section: [kodango@devops awk_temp]$ echo $'line1line2' | awk '{print;exit} END {print "exit.."}' line1exit.. The next statement is similar to sed's n command, which reads the next record and returns to the beginning of the script: [kodango@devops awk_temp]$ echo $'line1line2' | awk '{> print "Before next.."> print $0 > next> print "After next.."> }'Before next..line1Before next..line2 From the above it can be seen that the print statement following next will not be executed. The print and printf statements are the most used and they output the content to standard output. Note that in the print statement, there is a difference between the output variables with no commas: [kodango@devops awk_temp]$ echo "1 2" | awk '{print $1, $2}'1 2[kodango@devops awk_temp]$ echo "1 2" | awk '{print $1 $2}'12 When print output, the separator between fields can be redefined by OFS: [kodango@devops awk_temp]$ echo "1 2" | awk '{OFS=";";print $1,$2}'1;2 In addition, the print output can also be redirected to a file or a command: Print items > output-fileprint items >> output-fileprint items | command Assuming there is a file like this, the first column is the statement name, and the second column is the corresponding description: [kodango@devops awk_temp]$ cat column.txt statement|descriptiondelete|delete item from an arrayexit|exit from the awk processnext|read next input record and process Now we need to output the contents of the two columns into two files: statement.txt and description.txt: [kodango@devops awk_temp]$ awk -F'|' '{> print $1 > "statement.txt";> print $2 > "description.txt"> }' column.txt [kodango@devops awk_temp]$ cat statement. Txt statementdeleteexitnext[kodango@devops awk_temp]$ cat description.txt descriptiondelete item from an arrayexit from the awk processread next input record and process Here is an example of redirecting to a command. Suppose we want to sort the following files: [kodango@devops awk_temp]$ cat num.list 13295 You can redirect the content of the print to the "sort -n" command: [kodango@devops awk_temp]$ awk '{print | "sort -n"}' num.list 12359 The use of the printf command is similar to that of print, but it can also be redirected to a file or output, except that printf has more formatting strings than print. The printf syntax is similar to most languages ​​including bash's printf command, but it is not covered here. The functions of awk are divided into mathematical functions, string functions, I/O processing functions, and user-defined functions. The user-defined functions are also briefly introduced in the previous article. We will introduce these types of functions one by one. . Mathematical Functions The following mathematical functions are supported in awk: Atan2(y,x): Arc tangent function; Cos(x): cosine function; Sin(x): sine function; Exp(x): The exponential function of the natural logarithm e; Log(x): Calculates the logarithm to the logarithm of e; Sqrt(x): Absolute value function; Int(x): Converts a numeric value to an integer; Rand(): Returns a random number from 0 to 1, not including 1; Srand([expr]): Sets a random seed, generally used with the rand function. If the parameter is empty, the current time is used as the seed by default. For example, we use the rand() function to generate a random number: [kodango@devops awk_temp]$ awk 'BEGIN {print rand(),rand();}'0.237788 0.291066[kodango@devops awk_temp]$ awk 'BEGIN {print rand(),rand();}'0.237788 0.291066 However, you will find that each awk execution will generate the same random number, but the random number generated during one execution is different. Since every awk execution uses the same seed, we can use the srand() function to set the seed: [kodango@devops awk_temp]$ awk 'BEGIN {srand();print rand(),rand();}'0.171625 0.00692412[kodango@devops awk_temp]$ awk 'BEGIN {srand();print rand(),rand( );}'0.43269 0.782984 In this way, the random number generated each time is different. Using the rand() function we can also generate integers from 1 to n: [kodango@devops awk_temp]$ awk '> function randint(n) { return int(n*rand()); }> BEGIN { srand(); print randint(10);> }'3 String function Awk contains most of the common string manipulation functions. 1. sub(ere, repl[, in]) Description: Simply put, replace the part of in in match in ere with repl, and the return value is the number of substitutions. If the in parameter is omitted, $0 is used by default. Replaced actions directly modify the value of the variable. Here is a simple alternative example: [kodango@devops ~]$ echo "hello, world" | awk '{print sub(/ello/, "i"); print}'1hi, world In the repl parameter & is a metacharacter which indicates the content of the match, for example: [kodango@devops ~]$ awk 'BEGIN {var="kodango"; sub(/kodango/, "hello, &", var); print var}'hello, kodango 2. gsub(ere, repl[, in]) Description: Similar to sub () function, except that gsub () is a global replacement, that is to replace all matching content. 3. index(s, t) Description: Returns the position of the string t in s. Note that the position is calculated from 1 and returns 0 if it is not found. E.g: [kodango@devops ~]$ awk 'BEGIN {print index("kodango", "o")}'2[kodango@devops ~]$ awk 'BEGIN {print index("kodango", "w")}'0 4. length[([s])] Description: Returns the length of the string. If the parameter s is not specified, $0 is used as a parameter by default. E.g: [kodango@devops ~]$ awk 'BEGIN {print length('kodango');}'0[kodango@devops ~]$ echo "first line" | awk '{print length();}'10 5. match(s, ere) Description: Returns the starting position of the string s matching the ere, or 0 if they do not match. This function defines two built-in variables, RSTART and RLENGTH. RSTART is the same as the return value. RLENGTH records the length of the matching substring, or -1 if it does not match. E.g: [kodango@devops ~]$ awk 'BEGIN {print match("kodango", /dango/);printf "Matched at: %d, Matched substr length: %d", RSTART, RLENGTH;}'3Matched at: 3, Matched substr length: 5 6. split(s, a[, fs]) Description: The string is separated into multiple parts according to the separator fs, and stored in the array a. Note that the storage location starts from the first array element. If fs is empty, FS separation is used by default. The number of values ​​separated by the function's return value. E.g: [kodango@devops ~]$ awk 'BEGIN {> split("1;2;3;4;5", arr, ";")> for (i in arr)> printf "arr[%d]=%d ", i, arr[i];> }'arr[4]=4arr[5]=5arr[1]=1arr[2]=2arr[3]=3 One strange thing here is that the array of output for..in.. is not output in order. If you want to output in order, you can use a regular for loop: [kodango@devops ~]$ awk 'BEGIN {> split("1;2;3;4;5", arr, ";")> for (i=0;^C[kodango@devops ~]$ awk ' BEGIN {> n=split("1;2;3;4;5", arr, ";")> for (i=1; i<=n; i++)> printf "arr[%d]=%d ", i, arr[i];> }'arr[1]=1arr[2]=2arr[3]=3arr[4]=4arr[5]=5 7. sprintf(fmt, expr, expr, ...) Description: Similar to printf, except that the formatted content is not output to standard output, but is returned as the return value. E.g: [kodango@devops ~]$ awk 'BEGIN {> var=sprintf("%s=%s", "name", "value")> print var> }'name=value 8. substr(s, m[, n]) Description: Returns a substring of length n starting from position m, where position is calculated from 1 and if no value of n or n is greater than the remaining number of characters, the substring continues until the end of the string. E.g: [kodango@devops ~]$ awk 'BEGIN { print substr("kodango", 2, 3); }'oda[kodango@devops ~]$ awk 'BEGIN { print substr("kodango", 2); }'odango 9. tolower(s) Description: Converts a string to lowercase characters. E.g: [kodango@devops ~]$ awk 'BEGIN {print tolower("KODANGO");}'kodango 10. toupper(s) Description: Converts a string to uppercase characters. E.g [kodango@devops ~]$ awk 'BEGIN {print tolower("kodango");}'KODANGO I/O processing functions Getline The use of getline is relatively complicated. It has several different forms. However, its main function is to obtain one line of input at a time from the input. a. expression | getline [var] This form takes the result of the previous pipelined command output as the input to getline, one row at a time. If it is followed by var, the read is saved to the var variable, otherwise $0 and NF are reset. For example, we display the contents of the statement.txt file above as input to getline: [kodango@devops awk_temp]$ awk 'BEGIN { while("cat statement.txt" | getline var) print var}' statementdeleteexitnext In the above example, the command uses double quotation marks, "cat statement.txt", which is the same as print/printf. If you do not add var, write directly to $0, note that the NF value will also be updated: [kodango@devops awk_temp]$ awk 'BEGIN { while("cat statement.txt" | getline) print $0,NF}' statement 1delete 1exit 1next 1 b. getline [var] The second form is to use getline directly, which reads input from the processed file. Similarly, if var does not, $0 is set, and NF, NR, and FNR are updated at this time: [kodango@devops awk_temp]$ awk '{> while (getline) > print NF, NR, FNR, $0;> }' statement.txt1 2 2 delete1 3 3 exit1 4 4 next c. getline [var] < expression The third form redirects input from expression, similar to the first method, and it will not be repeated here. 2. close The close function can be used to close an already opened file or pipe. For example, the first form of the getline function uses a pipe. We can close the pipe with the close function. The parameters of the close function are the same as those of the pipe: [kodango@devops awk_temp]$ awk 'BEGIN {while("cat statement.txt" | getline) { print $0; close("cat statement.txt");}}'statementstatementstatementstatementstatement But after each line is read, closing the pipe, and then re-opening and re-reading the first line is an infinite loop. Therefore, it should be used with caution. Under normal circumstances, the close function is rarely used. 3. system This function is very simple, it is used to execute external commands, such as: [kodango@devops awk_temp]$ awk 'BEGIN {system("uname -r");}'3.6.2-1-ARCH
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ARGC Each of the command line parameters, ie the length of the ARGV array ARGV Store command line parameters CONVFMT Defines the format for converting awk internal values ​​to strings. The default value is "%.6g" OFMT Defines the format in which the value is converted to a string when output. The default value is "%.6g" ENVIRON An associative array of system environment variables FILENAME The current file name being processed NR The total number of records FNR The total number of records in the current file FS Field separator, default is blank NF The number of fields in each record RS Record separator, default is carriage return OFS Field delimiter when output, default is blank ORS Delimiter recorded when output, the default is carriage return RLENGTH The length of the substring matched by the match function RSTART The substring matched by the match function is at the start of the target string
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