How can replace a specific line in a text file with a shell script?

Question

I am trying to replace a specific line in a txt file with my shell script, for example;

cat aa.txt:
auditd=0
bladeServerSlot=0

When I run my script I would like to change "bladeServerSlot" to 12 as following;

cat aa.txt:
auditd=0
bladeServerSlot=12

Could you please help me?

Example : perl -ne '$_ =~ s/bladeServerSlot\=0/bladeServerSlot\=12/; print $_;' aa.txt — AbhiNickz
– AbhiNickz, Commented Feb 14, 2017 at 6:17
That could be written much nicer with perl -pe 's/bladeServerSlot=0/bladeServerSlot=12/' aa.txt. — Sobrique
– Sobrique, Commented Feb 14, 2017 at 9:27

Benjamin W. · Accepted Answer · 2017-02-14 06:32:04Z

3

Using sed and backreferencing:

sed -r '/bladeServerSlot/ s/(^.*)(=.*)/\1=12/g' inputfile

Using awk , this will search for the line which contains bladeServerSlot and replace the second column of that line.

awk  'BEGIN{FS=OFS="="}/bladeServerSlot/{$2=12}1' inputfile

edited Feb 14, 2017 at 6:32

Benjamin W.

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answered Feb 14, 2017 at 6:14

P....

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3 Comments

P.... Over a year ago

whoever downvoted, please have some courtesy to explain the reason for downvote.

William Pursell Over a year ago

Seems like the sed would be cleaner as /^bladeServerSlot/s/=.*$/=12/

WeiHua Liu Over a year ago

sed '/^bladeServerSlot/s/=.*$/=12/g' aa.txt > output.txt

zdim · Accepted Answer · 2017-02-14 19:13:31Z

2

perl -pe 's/bladeServerSlot=\K\d+/12/' aa.txt  > output.txt

The \K is a particular form of the positive lookbehind, which discards all previous matches. So we need to replace only what follows. The s/ is applied by default to $_, which contains the current line. The -p prints $_ for every line, so all other lines are copied. We redirect output to a file.

edited Feb 14, 2017 at 19:13

answered Feb 14, 2017 at 6:27

zdim

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Comments

Ronny Polley · Accepted Answer · 2017-02-14 18:39:12Z

-1

Is it really necessary to replace the line in your example? As bladeServerSlot is a variable you could reset the value.

bladeServerSlot=`any command`

Or you could just let this variable be filled by a Parameter provided to this script.

bladeServerSlot=$1

With $1being the first parameter of your script. I think this would be the cleaner way do solve your issue than to do fancy regex here. The sed/perl solutions will work, but they are not very clear to other people reading your script.

edited Feb 14, 2017 at 18:39

answered Feb 14, 2017 at 6:15

Ronny Polley

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