Print lines between two patterns , the awk way ...

12 Oct 2010

Post first published in nixtip

Example input file:

test -3
test -2
test -1
OUTPUT
top 2
bottom 1
left 0
right 0
page 66
END
test 1
test 2
test 3

The standard way ..

awk '/OUTPUT/ {flag=1;next} /END/{flag=0} flag {print}' infile

top 2
bottom 1
left 0
right 0
page 66

Self-explained indented code:

awk '
/OUTPUT/ {flag=1;next} # Initial pattern found --> turn on the flag and read the next line
/END/    {flag=0}      # Final pattern found   --> turn off rhe flag
flag     {print}       # Flag on --> print the current line
' infile

The first optimization is to get rid of the print , in awk when a condition is true print is the default action , so when the flag is true the line is going to be echoed.

To delete de NEXT statement , in order o prevent printing the TAG line, we need to activate the flag after the OUTPUT pattern discovery and after the flag evaluation.

A slight variation of the program flow and we’re done:

awk '/END/{flag=0}flag;/OUTPUT/{flag=1}' infile

PD: What if we only want to print the lines enclosed between the OUTPUT && END tags ?

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Print lines between two patterns , the awk way ...