awk - Unix, Linux Command

NAME

awk - Finds and Replaces text, database sort/validate/index

SYNOPSIS

awk 'Program' input-file1 input-file2 ... awk -f PROGRAM-FILE input-file1 input-file2 ...

DESCRIPTION

awk command searches files for text containing a pattern. When a line or text matches, awk performs a specific action on that line/text. The Program statement tells awk what operation to do; Program statement consists of a series of "rules" where each rule specifies one pattern to search for, and one action to perform when a particular pattern is found. A regular expression enclosed in slashes (/) is an awk pattern to match every input record whose text belongs to that set.

OPTIONS

Tag	Description
-F FS --field-separator FS	Use FS for the input field separator (the value of the 'FS' predefined variable).
-f PROGRAM-FILE --file PROGRAM-FILE	Read the awk program source from the file PROGRAM-FILE, instead of from the first command line argument.
-mf NNN -mr NNN	The 'f' flag sets the maximum number of fields, and the 'r' flag sets the maximum record size. These options are ignored by 'gawk', since 'gawk' has no predefined limits; they are only for compatibility with the Bell Labs research version of Unix awk.
-v VAR=VAL --assign VAR=VAL	Assign the variable VAR the value VAL before program execution begins.
-W traditional -W compat --traditional --compat	Use compatibility mode, in which 'gawk' extensions are turned off.
-W lint --lint	Give warnings about dubious or non-portable awk constructs.
-W lint-old --lint-old	Warn about constructs that are not available in the original Version 7 Unix version of awk.
-W posix --posix	Use POSIX compatibility mode, in which 'gawk' extensions are turned off and additional restrictions apply.
-W re-interval --re-interval	Allow interval expressions, in regexps.
-W source=PROGRAM-TEXT --source PROGRAM-TEXT	Use PROGRAM-TEXT as awk program source code. This option allows mixing command line source code with source code from files, and is particularly useful for mixing command line programs with library functions.
--	Signal the end of options. This is useful to allow further arguments to the awk program itself to start with a '-'. This is mainly for consistency with POSIX argument parsing conventions.
'Program'	A series of patterns and actions
Input-File	If no Input-File is specified then awk applies the Program to "standard input", (piped output of some other command or the terminal. Typed input will continue until end-of-file (typing 'Control-d')

EXAMPLES

To return the second item($2) from each line of the output from an ls - l listing.
```
$ ls -l | awk '{print $2}'
13
3
17
7
```
To print the Row Number (NR), then a dash and space ("- ") and then the first item ($1) from each line in sample.txt.

First create a sample.txt file
```
Sample Line 1
Sample Line 2
Sample Line 3
```
```
$ awk '{print NR "- " $1 }' sample.txt
1 - Sample
2 - Sample
3 - Sample
```
To print the first item ($1) and then the second last item $(NF-1) from each line in sample.txt.
```
$ awk '{print $1, $(NF-1) }' sample.txt
Sample Line
Sample Line
Sample Line
```
To print non-empty line from a file.
```
$ awk 'NF > 0' sample.txt
```

To print the length of the longest input line.

$ awk '{ if (length($0) > max) max = length($0) } END { print max }' sample.txt
13

To print seven random numbers from zero to 100, inclusive.

$  awk 'BEGIN { for (i = 1; i <= 7; i++) print int(101 * rand()) }'
24
29
85
15
59
19
81

To count the lines in a file
```
$ awk 'END { print NR }' sample.txt
3
```

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