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If grep pattern matching isn't behaving the way I expect, I turn to perl. Here's how to invoke regex pattern matching from a command line using perl:

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perl

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-n

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-e

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'print

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if

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$_=~/

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<pattern>/

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'

For example:

echo -e "12\n23\n4\n5" | perl -n -e 'print if $_ =~/\d\d/'

# or, for lines not matching
echo -e "12\n23\n4\n5" | perl -n -e 'print if $_ !~/\d\d/'

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If sed pattern substitution is not working as I expect (which happens frequently!), I again turn to perl. Here's how to invoke regex pattern substitution from a command line:

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perl

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-p

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-e

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'~s/<search

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pattern>/<replacement>/

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'

For example:

cat joblist.txt | perl -ne 'print if $_ =~/SA18\d\d\d$/' | \
  perl -pe '~s/JA/job /' | perl -pe '~s/SA/run /'

# Or, using parentheses to capture part of the search pattern:
cat joblist.txt | perl -ne 'print if $_ =~/SA18\d\d\d$/' | \
  perl -pe '~s/JA(\d+)\tSA(\d+)/job $1 - run $2/'

Gory details:

• -p tells perl to print its substitution results
• -e introduces the perl script (always encode it in single quotes to protect it from shell evaluation)
• ~s is the perl pattern substitution operator
• forward slashes ("/  /  /") enclose the regex search pattern and the replacement text

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