getting variable name in file name for bash

Question

I wanted to change the name of my file from file.txt to file_4i.txt and file_5i.txt according to the number I need but when I use the command below, the file name changes to file_.txt and the value of m never is indicated. I wanted to get 4i but $mi does not work either.

sudo sh -c "m=4 ; mv file.txt file_$mi.txt"
sudo sh -c "m=4 ; mv file.txt file_$m.txt"

score 0 · Answer 1 · answered Oct 25 '18 at 00:58

0

Use single quotes so the variable doesn't expand early, and use {} so mi isn't interpreted as the variable name:

sudo sh -c 'm=4 ; mv file.txt file_${m}i.txt'
sudo sh -c 'm=4 ; mv file.txt file_$m.txt'

answered Oct 25 '18 at 00:58

Joseph Sible-Reinstate Monica

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I get file_{4}i.txt not file_4i.txt by using your answer. – vkaul11 Oct 25 '18 at 01:03
@vkaul11 It works when I try it. What is sh on your system? For me, it's dash version 0.5.8-2.1ubuntu2. – Joseph Sible-Reinstate Monica Oct 25 '18 at 01:06
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@vkaul11 Also, are you sure you did `${m}` and not `{$m}`? – Joseph Sible-Reinstate Monica Oct 25 '18 at 01:07
`${m}` should work in any Bourne-style shell, that syntax has been around for ages. – Barmar Oct 25 '18 at 01:07
Yes you are right. But I was just confused about single quotes vs double quotes as I thought double quotes are needed to interpret variables. – vkaul11 Oct 25 '18 at 01:08
@vkaul11 They are, but you don't want the variable to be interpreted at first, since m isn't set until after that step. – Joseph Sible-Reinstate Monica Oct 25 '18 at 01:09

getting variable name in file name for bash

1 Answers1