Creating an empty file having a variable name in a script

Question

I need to create an empty file using a shell script. The filename will be determined by examining all the files in a directory matching a pattern, say TEST.*, and appending _END to it so that the new file might look like TEST.2011_END. Let the current directory be $DIR. So I tried:

for file in $DIR/TEST.*
do
    touch $file_END  
done

This gives an error. I also tried replacing touch $file_END with:

filename=$file_END  
touch $filename

but with no luck. What should I do?

touch is often used to create an empty file, but its primary purpose it to touch a file's timestamp... If a file with the name already exist, 'touch' will not make it become "empty".... If you want to force an existing file to be empty (thereby losing any data it contains), you can use cp /dev/null "${file}_END" which will either create an empty file if it doesn't currently exist, or if it does exist, it will truncate it to zero length (ie. empty)... — Peter.O, Apr 01 '11 at 15:42
@fred.bear: A common idiom to create or truncate a file is : >"${file}_END" — Gilles 'SO- stop being evil', Apr 01 '11 at 21:22

score 11 · Accepted Answer · edited Apr 01 '11 at 21:20

11

The syntax would be:

filename="${file}_END"

or in your code

touch "${file}_END"

The " quotes are not necessary as long as $file does not have any whitespace or globbing character in it.

edited Apr 01 '11 at 21:20

Gilles 'SO- stop being evil'

829,060

answered Apr 01 '11 at 12:03

Mat

52,586

3

Always put double quotes around variable substitutions unless you know you need field splitting and pathname expansion. This is a simpler and safer approach than trying to figure out whether they are strictly necessary. – Gilles 'SO- stop being evil' Apr 01 '11 at 21:21

score 2 · Answer 2 · answered Apr 01 '11 at 12:11

2

the command interpreter thinks you mean $file_END ( value of the variable named file_END ). you can work around this by quoting. The syntax could be:

filename="$file""_END"

or

filename="$file"_END

or even

filename=$file"_END"

though i prefer the first one for clarity!

answered Apr 01 '11 at 12:11

user6218

121

1

I consider "${file}_END" more clear still. – glenn jackman Apr 01 '11 at 15:01

Creating an empty file having a variable name in a script

2 Answers2