CODEWITHSUNDEEP
stringbashescapingbackslash
Nick Charney Kaye
Nick Charney Kaye

Reputation: 4340

How do I escape a series of backslashes in a bash printf?

The following script yielded an unexpected output:

printf "escaped slash: \\ \n"
printf "2 escaped slashes: \\\\ \n"
printf "3 escaped slashes: \\\\\\ \n"
printf "4 escaped slashes: \\\\\\\\ \n"

Run as a bash script under Ubuntu 14, I see:

escaped slash: \
2 escaped slashes: \ 
3 escaped slashes: \\ 
4 escaped slashes: \\

Err.. what?

Upvotes: 19

Views: 44977

Answers (3)

Kaiwen
Kaiwen

Reputation: 355

An additional note on what Cyrus said:

If you quote the printf's ARGUMENT with single quotes, you should save a lot of backslashes. For example,

printf "%s\n" 'escaped slash: \'
printf "%s\n" '2 escaped slashes: \\'
printf "%s\n" '3 escaped slashes: \\\'
printf "%s\n" '4 escaped slashes: \\\\'

outputs

1 escaped slash:   \
2 escaped slashes: \\
3 escaped slashes: \\\
4 escaped slashes: \\\\

Upvotes: 3

Cyrus
Cyrus

Reputation: 88583

printf is a bash builtin. Look at help printf:

printf [-v var] format [arguments]
      Formats and prints ARGUMENTS under control of the FORMAT.

You should pass the format and the argument. So add the format "%s\n" before the argument:

printf "%s\n" "escaped slash: \\"
printf "%s\n" "2 escaped slashes: \\\\"
printf "%s\n" "3 escaped slashes: \\\\\\"
printf "%s\n" "4 escaped slashes: \\\\\\\\"

Output:

escaped slash: \ 
2 escaped slashes: \\ 
3 escaped slashes: \\\ 
4 escaped slashes: \\\\

Upvotes: 6

Eugeniu Rosca
Eugeniu Rosca

Reputation: 5305

Assuming that printf FORMAT string is surrounded by double quotes, printf takes one additional level of expansion, compared to e.g. echo (both being shell builtin commands).

What you expect from printf can actually be achieved using single quotes:

printf '1 escaped slash:   \\ \n'
printf '2 escaped slashes: \\\\ \n'
printf '3 escaped slashes: \\\\\\ \n'
printf '4 escaped slashes: \\\\\\\\ \n'

outputs:

1 escaped slash:   \
2 escaped slashes: \\
3 escaped slashes: \\\
4 escaped slashes: \\\\

Upvotes: 13

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