How to replace string into numbers using sed?

Question

I am trying to replace string into number from the file So, I have variable &FLOW which need to change to 001, ex :

cat file.txt
This is file ' PISP &FLOW'
PISD.DATA.CYCLE&FLOW..ONE

desired output

This is file ' PISP 001'
PISD.DATA.CYCLE001.ONE

I tried below commands in a script :

for item in file.txt
do
sed 's/\&FLOW/\./001/g' $item
sed 's/\&FLOW/001/g' $item
done

It is giving error. The second sed command is working, but I need to run first the beginning sed command otherwise after running first the second sed command, it would ignore the beginning sed command.

Any help would be appreciated!

You set item to to literal string filename, but the file you show as example input is called file.txt, so that won't work, for starters. — Benjamin W.
– Benjamin W., Commented May 30, 2019 at 17:34
Thank you for reply, I changed into file.txt. It is still not working — flow
– flow, Commented May 30, 2019 at 17:37
@JNevill it supposed to change from two dots into one after variable — flow
– flow, Commented May 30, 2019 at 17:39
First of all, you do not need to use two sed commands, you may chain them like sed 's/1/2/g;s/3/4/g'. However, your patterns are so similar, they only differ in 1 char, so you may make it optional and use a single pattern. More importantly, you did not actually modify file contents, you need to pass the -i (inline) option. See my answer below with explanations of the pattern and how to use -i with both Linux (GNU) and Mac OS (FreeBSD) sed. — Wiktor Stribiżew
– Wiktor Stribiżew, Commented May 30, 2019 at 21:14

Wiktor Stribiżew · Accepted Answer · 2019-05-30 21:16:31Z

1

Use a single sed command and use -i to actually modify the file contents and you need to pass file.txt as the input for the sed command:

sed -i 's/&FLOW\.\{0,1\}/001/g' file.txt

See the online demo. If you are using it in Mac OS, you need sed -i '' 's/&FLOW\.\{0,1\}/001/g' file.txt. Also see sed edit file in place.

Pattern details

It is a POSIX BRE compliant pattern matching

&FLOW - a literal &FLOW substring
\.\{0,1\} - 0 or 1 occurrence of a . char.

edited May 30, 2019 at 21:16

answered May 30, 2019 at 21:02

Wiktor Stribiżew

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1 Comment

Wiktor Stribiżew Over a year ago

@flow If you have any related questions, please feel free to ask.

Dudi Boy · Accepted Answer · 2019-05-30 21:07:23Z

1

try this:

for item in file.txt
do
  sed 's/\&FLOW\./001/g' $item
  sed 's/\&FLOW/001/g' $item
done

You had a redundant / in after FLOW

This might also work:

  sed -i 's/\&FLOW[\.]?/001/g' file.txt

edited May 30, 2019 at 21:07

answered May 30, 2019 at 21:00

Dudi Boy

1

3 Comments

flow Over a year ago

Thank you for response! I have a question, what ? is for?

Dudi Boy Over a year ago

? is a conditional match for 0 or 1 occurrence of . character. If this is correct answer, please mark it as such.

Ed Morton Over a year ago

? is an ERE metachar, it won't work in sed (which uses BREs) unless you add -E to enable EREs (GNU sed and OSX/BSD sed which you're probably using for -i anyway). Or you can use the POSIX BRE equivalent of \{0,1\}.

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