Finding a string between two lines in a file using linux commands

Question

I have a file, file.txt, like this:

start cal
end cal
start eff
end eff
start cal
error
end cal
start dod
end dod

What I want to get is the line between the last set of 'start cal' and 'end cal'. I am using tac and grep to do it. But in vain. Any help please? Below is my code:

tac file.txt | grep -m1 'start cal*end cal'

What am I doing wrong? For the example above, I need the command to return 'error'.

Kent · Accepted Answer · 2016-06-17 12:12:30Z

1

Grep is not good tool for this task. It does line based matching. You can consider using awk.

if you have single line in between:

tac file|awk '/end cal/{p=1;next}/start cal/{exit}p'

If it could be multiple lines:

tac file|awk '/end cal/{p=1;next}/start cal/{exit}p'|tac

It outputs:

error

answered Jun 17, 2016 at 12:12

Kent

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3 Comments

nephtes Over a year ago

Beat me by 13 seconds! What's that /pattern/ { commands } variable syntax? I don't recognize it.

Kent Over a year ago

I don't understand your question. sorry.. :-( @nephtes

nephtes Over a year ago

Oh, never mind, I misread. It's a condition for the default rule. Avoids the "if (echo) print" in my solution.

nephtes · Accepted Answer · 2016-06-17 13:17:41Z

1

I don't know if grep can do it, but here it is in gawk. I'll be the first to admit, it's not exactly pretty.

tac file.txt | gawk '/start cal/ { exit } { if (echo) print } /end cal/ { echo = 1 }'

n.b. Kent's answer is better polished.

edited Jun 17, 2016 at 13:17

answered Jun 17, 2016 at 12:12

nephtes

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Comments

melpomene · Accepted Answer · 2016-06-17 12:12:53Z

0

You're doing two things wrong:

grep examines each line separately, so a pattern can never match across two or more lines
the regex start cal*end cal matches start ca, followed by 0 or more ls, followed by end cal

answered Jun 17, 2016 at 12:12

melpomene

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