Short way to escape HTML in Bash?

Question

The box has no Ruby/Python/Perl etc.

Only bash, sed, and awk.

A way is to replace chars by map, but it becomes tedious.

Perhaps some built-in functionality i'm not aware of?

Answer 1

Escaping HTML really just involves replacing three characters: <, >, and &. For extra points, you can also replace " and '. So, it's not a long sed script:

sed 's/&/\&amp;/g; s/</\&lt;/g; s/>/\&gt;/g; s/"/\&quot;/g; s/'"'"'/\&#39;/g'

Answer 2

You can use recode utility:

    echo 'He said: "Not sure that - 2<1"' | recode ascii..html

Output:

    He said: "Not sure that - 2<1"

Answer 3

Pure bash, no external programs:

function htmlEscape () {
    local s
    s=${1//&/&}
    s=${s//</&lt;}
    s=${s//>/&gt;}
    s=${s//'"'/&quot;}
    printf -- %s "$s"
}

Just simple string substitution.

Answer 4

or use xmlstar Escape/Unescape special XML characters:

$ echo '<abc&def>'| xml esc
&lt;abc&amp;def&gt;

Answer 5

I'm using jq:

$ echo "2 < 4 is 'TRUE'" | jq -Rr @html
2 &lt; 4 is &apos;TRUE&apos;

Answer 6

This is an updated answer to miken32 "Pure bash, "no external programs":

bash 5.2 breaks backward compatibility in ways that are highly inconvenient.

From NEWS:

x. New shell option: patsub_replacement. When enabled, a '&' in the replacement string of the pattern substitution expansion is replaced by the portion of the string that matched the pattern. Backslash will escape the '&' and insert a literal '&'.

The option is enabled by default. If you want to restore the previous behavior, add shopt -u patsub_replacement.

So there is three ways to use miken32 code in bash 5.2+:

Either disable patsub_replacement:

shopt -u patsub_replacement
function htmlEscape () {
    local s
    s=${1//&/&}
    s=${s//</&lt;}
    s=${s//>/&gt;}
    s=${s//'"'/&quot;}
    printf -- %s "$s"
}

, another option is to escape '&' with backslash in the replacement if you want to make it work regardless of the 5.2 feature, patsub_replacement:

function htmlEscape () {
    local s
    s=${1//&/\&}
    s=${s//</\&lt;}
    s=${s//>/\&gt;}
    s=${s//'"'/\&quot;}
    printf -- %s "$s"
}

and another option is to quote string in the replacement:

function htmlEscape () {
    local s
    s=${1//&/"&"}
    s=${s//</"&lt;"}
    s=${s//>/"&gt;"}
    s=${s//'"'/"&quot;"}
    printf -- %s "$s"
}

Answer 7

There's much better answers, but I just found this so I thought I'd share.

PN=`basename "$0"`          # Program name
VER=`echo '$Revision: 1.1 $' | cut -d' ' -f2`

Usage () {
    echo >&2 "$PN - encode HTML unsave characters, $VER
usage: $PN [file ...]"
    exit 1
}

set -- `getopt h "$@"`
while [ $# -gt 0 ]
do
    case "$1" in
    --) shift; break;;
    -h) Usage;;
    -*) Usage;;
    *)  break;;         # First file name
    esac
    shift
done

sed                                     \
    -e 's/&/\&/g'                       \
    -e 's/"/\"/g'                      \
    -e 's/</\&lt;/g'                        \
    -e 's/>/\&gt;/g'                        \
    -e 's/„/\&auml;/g'                      \
    -e 's/Ž/\&Auml;/g'                      \
    -e 's/”/\&ouml;/g'                      \
    -e 's/™/\&Ouml;/g'                      \
    -e 's//\&uuml;/g'                       \
    -e 's/š/\&Uuml;/g'                      \
    -e 's/á/\&szlig;/g'                     \
    "$@"

Answer 8

The previous sed replacement defaces valid output like

<

into

<

Adding a negative loook-ahead so "&" is only changed into "&" if that "&" isn't already followed by "amp;" fixes that:

sed 's/&(?!amp;)/\&amp;/g; s/</\&lt;/g; s/>/\&gt;/g; s/"/\&quot;/g; s/'"'"'/\&#39;/g'