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Accepted
Josef Klimuk
Asked: 2018-05-17 03:18:53 +0800 CST

How do I get the exit status when using the sed command?

  • 772

The grep command gives out an exit status:

$echo "foo.bar" | grep -o foo
foo
$echo $?
0
$echo "foo.bar" | grep -o pop
$echo $?
1

But I need to use sed and I realized that it has no exit status:

$echo "foo.bar" | sed 's/bar.*$//'
foo.
$echo $?
0
$echo "foo.bar" | sed 's/pop.*$//'
foo.bar
$echo $?
0

I know that I should play around with the -q option, but I have not succeeded.

command-line sed

3 Answers

  1. Best Answer

    You can use qn to quit with exit status n - but to make that useful, you will also need to use some Branching and Flow Control:

    t
    branch conditionally (that is: jump to a label) only if a s/// command has succeeded since the last input line was read or another conditional branch was taken.

    It is probably best to choose a value for n that is distinct from one of the standard exit status values:

    An exit status of zero indicates success, and a nonzero value indicates failure. GNU 'sed' returns the following exit status error values:

    0
 Successful completion.

1
 Invalid command, invalid syntax, invalid regular expression or a
 GNU 'sed' extension command used with '--posix'.

2
 One or more of the input file specified on the command line could
 not be opened (e.g.  if a file is not found, or read permission is
 denied).  Processing continued with other files.

4
 An I/O error, or a serious processing error during runtime, GNU
 'sed' aborted immediately.

    So for example

    $ echo "foo.bar" | sed 's/bar.*$//; t; q42' ; echo $? 
foo.
0

    whereas

    $ echo "foo.bar" | sed 's/baz.*$//; t; q42' ; echo $? 
foo.bar
42

    If you want to omit the default printing of the pattern space, then replace q by Q (note that Q is a GNU extension).

    • 14

  2. Here's how to search regex with sed, and highlight matches, or return exit code (5) if no match found:

    This is input.txt:

    hello there
my dear old friend
a lot of things
we'll pass along the end

    Here's my function to Print all + Highlight matches + Return exit code:

    highlight()
{
  pattern=$1
  shift
  sed '/'"${pattern}"'/,${s//\x1b[32m&\x1b[0m/g;b};$q5' "$@"
}

    $ highlight "lo\|end" input.txt || echo -e "\n* No match found *"

    hello there
    my dear old friend
    a lot of things
    we'll pass along the end

    When there's no match, it will return exit code (5). You can use it with cat and pipe | as well:

    $ cat input.txt | highlight "hot\|and" || echo -e "\n* No match found *"

    hello there
    my dear old friend
    a lot of things
    we'll pass along the end

    * No match found *

    Thanks to https://unix.stackexchange.com/a/405725/43233 - I'm using it + sed quit option.

    • 1

  3. duplicate of answer https://stackoverflow.com/a/61808364/10440128

    #!/bin/sh

read -d '' input <<EOF
a
b
EOF

echo "replace yes:"
echo "$input" >input.txt
sed -i 's/a/x/ w /dev/stdout' input.txt

echo "replace no:"
echo "$input" >input.txt
sed -i 's/z/x/ w /dev/stdout' input.txt

    output:

    replace yes:
x
replace no:

    so, to check if sed did replace something:

    #!/bin/sh

read -d '' input <<EOF
a
b
EOF

echo "$input" >input.txt
if [ -z "$(sed -i 's/a/x/w /dev/stdout' input.txt)" ]
then echo "replace no" # -z = "zero string"
else echo "replace yes"
fi

echo "$input" >input.txt
if [ -n "$(sed -i 's/z/x/w /dev/stdout' input.txt)" ]
then echo "replace yes" # -n = "nonzero string"
else echo "replace no"
fi

    output:

    replace yes
replace no

    limitation: can handle only one substitution. so this does not work:

    sed -i 's,a,b, w /dev/stdout ; s,b,a, w /dev/stdout' input.txt

    error:

    sed: couldn't open file /dev/stdout ; s,b,a, w /dev/stdout: No such file or directory

    (sed treats everything after w as a file path)

    workaround: use multiple sed calls

    #!/bin/sh

read -d '' input <<EOF
a
b
EOF

echo "$input" >input.txt
if [ -n "$(
  sed -i 's/a/x/w /dev/stdout' input.txt &&
  sed -i 's/x/a/w /dev/stdout' input.txt
)" ]
then echo "replace yes"
else echo "replace no"
fi
    • 0