Bash and filenames with spaces

Question

The following is a simple Bash command line:

grep -li \'regex\' \"filename with spaces\" \"filename\"

No problems. Also the following works

Answer 1

Try this:

(IFS=$'\n'; grep -li 'regex' $(<listOfFiles.txt))

IFS is the Internal Field Separator. Setting it to $'\n' tells Bash to use the newline character to delimit filenames. Its default value is $' \t\n' and can be printed using cat -etv <<<"$IFS".

Enclosing the script in parenthesis starts a subshell so that only commands within the parenthesis are affected by the custom IFS value.

Answer 2

cat listOfFiles.txt |tr '\n' '\0' |xargs -0 grep -li 'regex'

The -0 option on xargs tells xargs to use a null character rather than white space as a filename terminator. The tr command converts the incoming newlines to a null character.

This meets the OP's requirement that grep not be invoked multiple times. It has been my experience that for a large number of files avoiding the multiple invocations of grep improves performance considerably.

This scheme also avoids a bug in the OP's original method because his scheme will break where listOfFiles.txt contains a number of files that would exceed the buffer size for the commands. xargs knows about the maximum command size and will invoke grep multiple times to avoid that problem.

A related problem with using xargs and grep is that grep will prefix the output with the filename when invoked with multiple files. Because xargs invokes grep with multiple files one will receive output with the filename prefixed, but not for the case of one file in listOfFiles.txt or the case of multiple invocations where the last invocation contains one filename. To achieve consistent output add /dev/null to the grep command:

cat listOfFiles.txt |tr '\n' '\0' |xargs -0 grep -i 'regex' /dev/null

Note that was not an issue for the OP because he was using the -l option on grep; however it is likely to be an issue for others.

Answer 3

This works:

while read file; do grep -li dtw "$file"; done < listOfFiles.txt

Answer 4

Do note that if you somehow ended up with a list in a file which has Windows line endings, \r\n, NONE of the notes above about the input file separator $IFS (and quoting the argument) will work; so make sure that the line endings are correctly \n (I use scite to show the line endings, and easily change them from one to the other).

Also cat piped into while file read ... seems to work (apparently without need to set separators):

cat <(echo -e "AA AA\nBB BB") | while read file; do echo $file; done

... although for me it was more relevant for a "grep" through a directory with spaces in filenames:

grep -rlI 'search' "My Dir"/ | while read file; do echo $file; grep 'search\|else' "$ix"; done

Answer 5

With Bash 4, you can also use the builtin mapfile function to set an array containing each line and iterate on this array:

$ tree
.
├── a
│   ├── a 1
│   └── a 2
├── b
│   ├── b 1
│   └── b 2
└── c
    ├── c 1
    └── c 2

3 directories, 6 files
$ mapfile -t files < <(find -type f)
$ for file in "${files[@]}"; do
> echo "file: $file"
> done
file: ./a/a 2
file: ./a/a 1
file: ./b/b 2
file: ./b/b 1
file: ./c/c 2
file: ./c/c 1

Answer 6

Though it may overmatch, this is my favorite solution:

grep -i 'regex' $(cat listOfFiles.txt | sed -e "s/ /?/g")