CODEWITHSUNDEEP
linuxbashshellsed
jspiegelbe
jspiegelbe

Reputation: 51

Using STDIN from pipe in sed command to replace value in a file

I've got a command to perform a series of commands that produce a variable output string such as 123456. I want to pipe that to a sed command replacing a known string in a csv file that looks like this: Fred,Wilma,Betty,Barney

However, the command below does not work and I haven't found any other references to using pipe values as the variable for a replace.

How does this code change if the values in the csv are in a random order and I always want to change the second value?

Example code:

find / -iname awk 2>/dev/null | sha256sum | cut -c1-10 > test.txt | 
sed -i -e '/Wilma/ r test.txt' -e 's/Wilma//' input.csv

Contents of input.csv should become: Fred,0d522cd316,Betty,Barney

Upvotes: 5

Views: 6698

Answers (2)

agc
agc

Reputation: 8406

  1. For replacing a fixed string like "Wilma", try:

    sed -i 's/Wilma/'"$(find / -iname awk 2>/dev/null | 
                    sha256sum | cut -c1-10)"'/' input.csv

  2. To replace the 2nd field no matter what's in it, try:

    sed -i 's/[^,]*/'"$(find / -iname awk 2>/dev/null | 
                    sha256sum | cut -c1-10)"'/2' input.csv

Upvotes: 4

Chad Miller
Chad Miller

Reputation: 1475

Okay, in

find / -iname awk 2>/dev/null | sha256sum | cut -c1-10 > test.txt | sed -i -e '/Wilma/ r test.txt' -e 's/Wilma//' input.csv

you have a bug. That "> test.txt" after cut is going to eat your stdin on sed, so things go weird with that pipe afterwards taking stdin. You don't want a pipe there, or you don't want to redirect to a file.

The way to take piped stdin and use it as a parameter in a command is through xargs.

find / -iname awk 2>/dev/null | sha256sum | cut -c1-10 | xargs --replace=INSERTED -- sed -i -e 's/Wilma/INSERTED/' input.csv

(...though that find|shasum is suspect too, in that the order of files is random(ish) and it matters for a reliable sum. You prpobably mean to "|sort" after find.)

(Some would sed -i -e "s/Wilma/$(find|sort|shasum|cut)" f, but I ain't among them. Animals.)

Upvotes: 5

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