Shell script: single quote escaping

Question

I have following (part) of a shell script (inside t7508-status.sh):

test_expect_success 'status --column' '
    cat >expect <<\EOF &&
# On branch main
# Your branch and '\''upstream'\'' have diverged,
# and have 1 and 2 different commits each, respectively.
#   (use "git pull" to merge the remote branch into yours)
#
# Changes to be committed:
#   (use "git restore --staged <file>..." to unstage)
#   new file:   dir2/added
#
# Changes not staged for commit:
#   (use "git add <file>..." to update what will be committed)
#   (use "git restore <file>..." to discard changes in working directory)
#   modified:   dir1/modified
#
# Untracked files:
#   (use "git add <file>..." to include in what will be committed)
#   dir1/untracked dir2/untracked
#   dir2/modified  untracked
#
EOF
    COLUMNS=50 git -c status.displayCommentPrefix=true status --column="column dense" >output &&
    test_cmp expect output
'

OK, the first quoted part seems obvious status --column, but the second quoted parts starts at the end of the first line and ends IMHO in the third line

# Your branch and '\''upstream'\'' have diverged,
                  ^--here

Then an escaped quote follows by a new quoted part? Or does the <<\EOF ... EOF has higher priority? The reason for my question is to create correct syntax coloring using ANTLR.

The heredoc is inside the string so it does nothing, while `'\''` _inserts_ a literal `'` in the string — Fravadona, Jan 07 '22 at 18:37
Note that quoting is _per-character_. `'foo'"bar"baz` is all one string `foobarbaz` with subsets interpreted per different contexts' rules. That said, a regular single-quoted context recognizes _absolutely nothing_ as syntax except a single quote (as opposed to an ANSI C-like context; `$'...'` recognizes backslash escape sequences as special, including escapes that escape single-quotes). — Charles Duffy, Jan 07 '22 at 18:58
So `'won\'t'` would be illegal, but `'won'\''t'` be correct? — Thomas S., Jan 08 '22 at 12:55
The canonical is probably *[How to escape single quotes within single quoted strings](https://stackoverflow.com/questions/1250079/)* (2009. 26 answers. 1380 votes). — Peter Mortensen, Aug 16 '23 at 19:28

score 2 · Accepted Answer · answered Jan 07 '22 at 18:48

You are correct: the first quoted part ends on the third line, and is immediately followed by an escaped single-quote which is followed by another single-quoted section. Then the same thing happens again 8 characters later. Since there's no space or other delimiter between these sections, they're treated as parts of a single long string (an argument to test_expect_success).

Since the <<\EOF and # marks occur inside single-quoted sections, they have no syntactic significance at all; they are just literal characters that'll be passed to test_expect_success as part of the argument. In a single-quoted string, only thing with any syntactic significance is a single-quote (which just indicates the end of the single-quoted section).

You can see the result of this by replacing the test_expect_success command with printf '[%s]\n', and seeing what gets printed inside the [ ] marks.

Shell script: single quote escaping

1 Answers1