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linuxgrepaixhp-uxsunos

Grep "-C" command on all machine

I am using grep -C 1 "matching string" "xty.pom"

This works on Linux machines, but the same code is not working on other platforms like AIX, SunOS_x64, HPUX.

Is there any alternative to this so that same code logic works on all the platforms?

Solution

  • This will function like grep -C 1 "matching string" but should work on platforms that do not support grep's -C option:

    awk '/matching string/{print last; f=2} f{print; f--} {last=$0}' File

    How it works

    • /matching string/{print last; f=2}

      If the current line matches the regex matching string, then print the previous line (which was saved in last) and set f to 2.

    • f{print; f--}

      If f is nonzero, then print the current line and decrement f.

    • last=$0

      Set last equal to the contents of the current line.

    Improvement

    With some minor changes, we can handle overlapping matches better:

    awk '/a/{if (NR>1 && !f)print last; f=3} f>1{print} f{f--} {last=$0}'

    As an example of output with an overlapping match:

    $ printf '%s\n'   a a b |  awk '/a/{if (NR>1 && !f)print last; f=3} f>1{print} f{f--} {last=$0}'
a
a
b

    Sun/Solaris

    The native awk on Sun/Solaris is notoriously bug-filled. Use instead nawk or better yet /usr/xpg4/bin/awk or /usr/xpg6/bin/awk