6.2.1 Input from Files - awk - h0ng123 linux,oracle.unix

In the following examples, the percent sign is a shell prompt. Please take note: In all examples where the command is nawk, use either awk or gawk if you are on an HP-UX flavor system or using Linux.

FORMAT

% nawk 'pattern' filename

% nawk '{action}' filename

% nawk 'pattern {action}' filename

Here is a sample file called employees:

Example 6.1.

% cat employees

Tom Jones             4424    5/12/66                543354

Mary Adams            5346    11/4/63                28765

Sally Chang           1654    7/22/54                650000

Billy Black           1683    9/23/44                336500



% nawk '/Mary/'  employees

Mary Adams            5346    11/4/63                28765

EXPLANATION

Nawk prints all lines that contain the pattern Mary.

Example 6.2.

% cat employees

Tom Jones             4424    5/12/66                543354

Mary Adams            5346    11/4/63                28765

Sally Chang           1654    7/22/54                650000

Billy Black           1683    9/23/44                336500



% nawk '{print $1}' employees

Tom

Mary

Sally

Billy

EXPLANATION

Nawk prints the first field of file employees, where the field starts at the left margin of the line and is delimited by whitespace.

Example 6.3.

% cat employees

Tom Jones             4424    5/12/66              543354

Mary Adams            5346    11/4/63              28765

Sally Chang           1654    7/22/54              650000

Billy Black           1683    9/23/44              336500



% nawk '/Sally/{print $1, $2}' employees

Sally Chang

EXPLANATION

Nawk prints the first and second fields of file employees, only if the line contains the pattern Sally. Remember, the field separator is whitespace.

6.2.2 Input from Commands

The output from a UNIX/Linux command or commands can be piped to awk for processing. Shell programs commonly use awk for manipulating commands.

FORMAT

% command | nawk 'pattern'

% command | nawk '{action}'

% command | nawk 'pattern {action}'

Example 6.4.

1   % df | nawk '$4 > 75000'

    /oracle   (/dev/dsk/c0t0d057 ):390780 blocks     105756 files

    /opt    (/dev/dsk/c0t0d058 ):1943994 blocks      49187 files



2   % rusers  | nawk '/root$/{print  $1}'

    owl

    crow

    bluebird

EXPLANATION

The df command reports the free disk space on file systems. The output of the df command is piped to nawk. If the fourth field is greater than 75,000 blocks, the line is printed.
The rusers command prints those logged on remote machines on the network. The output of the rusers command is piped to nawk as input. The first field is printed if the regular expression root is matched at the end of the line ($); that is, all machine names are printed where root is logged on.