What is the correct way to escape a dollar sign in a bash regex? I am trying to test whether a string begins with a dollar sign. Here is my code, in which I double escape the dollar within my double quotes expression:
echo -e "AB1\nAB2\n\$EXTERNAL_REF\nAB3" | while read value;
do
if [[ ! $value =~ "^\\$" ]];
then
echo $value
else
echo "Variable found: $value"
fi
done
This does what I want for one box which has:
GNU bash, version 3.2.25(1)-release (x86_64-redhat-linux-gnu)
And the verbose output shows
+ [[ ! $EXTERNAL_REF =~ ^\$ ]]
+ echo 'Variable found: $EXTERNAL_REF'
However, on another box which uses
GNU bash, version 4.1.2(1)-release (x86_64-redhat-linux-gnu)
The comparison is expanded as follows
+ [[ ! $EXTERNAL_REF =~ \^\\\$ ]]
+ echo '$EXTERNAL_REF'
Is there a standard/better way to do this that will work across all implementations?
Many thanks
Why do you use a regular expression here? A glob is enough:
#!/bin/bash
while read value; do
if [[ "$value" != \$* ]]; then
echo "$value"
else
echo "Variable found: $value"
fi
done < <(printf "%s\n" "AB1" "AB2" '$EXTERNAL_REF' "AB3")
Works here with shopt -s compat32.
The regex doesn't need any quotes at all. This should work:
if [[ ! $value =~ ^\$ ]];
I would replace the double quotes with single quotes and remove a single \ and have the changes as below
$value =~ "^\\$"
can also be used as
$value =~ '^\$'
I never found the solution either, but for my purposes, I settled on the following workaround:
if [[ "$value" =~ ^(.)[[:alpha:]_][[:alnum:]_]+\\b && ${BASH_REMATCH[1]} == '$' ]]; then
echo "Variable found: $value"
else
echo "$value"
fi
Rather than trying to "quote" the dollar-sign, I instead match everything around it and I capture the character where the dollar-sign should be to do a direct-string comparison on. A bit of a kludge, but it works.
Alternatively, I've taken to using variables, but just for the backslash character (I don't like storing the entire regex in a variable because I find it confusing for the regex to not appear in the context where it's used):
bs="\\"
string="test\$test"
if [[ "$string" =~ $bs$ ]]; then
echo "output \"$BASH_REMATCH\""
fi
Related
From a variable how to extract integers that will be in format *\d+.\d+.\d+* (4.12.3123) using bash.
filename="xzxzxzxz4.12.3123fsfsfsfsfsfs"
I have tried:
filename="xzxzxzxz4.12.3123fsfsfsfsfsfs"
if [[ "$filename" =~ (.*)(\d+.\d+.\d+)(.*) ]]; then
echo ${BASH_REMATCH}
echo ${BASH_REMATCH[1]}
echo ${BASH_REMATCH[2]}
echo ${BASH_REMATCH[3]}
else
echo 'nej'
fi
which does not work.
The easiest way to work with regexes in Bash, in terms of consistency between Bash versions and escaping, is to put the regex into a single-quoted variable and then use it unquoted, as below:
re='[0-9]+\.[0-9]+\.[0-9]+'
[[ $filename =~ $re ]] && printf '%s\n' "${BASH_REMATCH[#]}"
The main issue with your approach were that you were using the "Perl-style" \d, so in fact you could make your code work with:
if [[ "$filename" =~ (.*)([0-9]+\.[0-9]+\.[0-9]+)(.*) ]]; then
echo "${BASH_REMATCH[2]}"
fi
But this unnecessarily creates 3 capture groups, when you don't even need one. Note that I also changed . (any character) to \. (a literal .).
one way to extract:
grep -oP '\d\.\d+\.\d+' <<<$xfilename
There is one more way
$ filename="xzxzxzxz4.12.3123fsfsfsfsfsfs"
$ awk '{ if (match($0, /[0-9].[0-9]+.[0-9]+/, m)) print m[0] }' <<< "$filename"
4.12.3123
I have a file (file.txt) that contains some text like:
000000000+000+0+00
000000001+000+0+00
000000002+000+0+00
and I am trying to check each line to make sure that it follows the format:
character*9, "+", character*3, "+", etc
so far I have:
#!/bin/ksh
file=file.txt
line_number=1
for line in $(cat $file)
do
if [[ "$line" != "[[.]]{9}+[[.]]{3}+[[.]]{1}+[[.]]{2} ]" ]]
then
echo "Invalid number ($line) check line $line_number"
exit 1
fi
let "line_number++"
done
however this does not evaluate correctly, no matter what I put in the lines the program terminates.
When you want line numbers of the mismatches, you can use grep -vn. Be careful with writing a correct regular expression, and you will have
grep -Evn "^.{9}[+].{3}[+].[+].{2}$" file.txt
This is not in the layout that you want, so change the layout with sed:
grep -Evn "^.{9}[+].{3}[+].[+].{2}$" file.txt |
sed -r 's/([^:]*):(.*)/Invalid number (\2) check line number \1./'
EDIT:
I changed .{1} into ..
The sed is also over the top. When you need spme explanation, you can start with echo "Linenr:Invalid line"
I'm having funny results putting the regex in the condition directly:
$ line='000000000+000+0+00'
$ [[ $line =~ ^.{9}\+.{3}\+.\+..$ ]] && echo ok
ksh: syntax error: `~(E)^.{9}\+.{3}\+.\+..$ ]] && echo ok
' unexpected
But if I save the regex in a variable:
$ re="^.{9}\+.{3}\+.\+..$"
$ [[ $line =~ $re ]] && echo ok
ok
So you can do
#!/bin/ksh
file=file.txt
line_number=1
re="^.{9}\+.{3}\+.\+..$"
while IFS= read -r line; do
if [[ ! $line =~ $re ]]; then
echo "Invalid number ($line) check line $line_number"
exit 1
fi
let "line_number++"
done < "$file"
You can also use a plain glob pattern:
if [[ $line != ?????????+???+?+?? ]]; then echo error; fi
ksh glob patterns have some regex-like syntax. If there's an optional space in there, you can handle that with the ?(sub-pattern) syntax
pattern="?????????+???+?( )?+??"
line1="000000000+000+0+00"
line2="000000000+000+ 0+00"
[[ $line1 == $pattern ]] && echo match || echo no match # => match
[[ $line2 == $pattern ]] && echo match || echo no match # => match
Read the "File Name Generation" section of the ksh man page.
Your regex looks bad - using sites like https://regex101.com/ is very helpful. From your description, I suspect it should look more like one of these;
^.{9}\+.{3}\+.{1}\+.{2}$
^[^\+]{9}\+[^\+]{3}\+[^\+]{1}\+[^\+]{2}$
^[0-9]{9}\+[0-9]{3}\+[0-9]{1}\+[0-9]{2}$
From the ksh manpage section on [[ - you would probably want to be using =~.
string =~ ere
True if string matches the pattern ~(E)ere where ere is an extended regular expression.
Note: As far as I know, ksh regex doesn't follow the normal syntax
You may have better luck with using grep:
# X="000000000+000+0+00"
# grep -qE "^[^\+]{9}\+[^\+]{3}\+[^\+]{1}\+[^\+]{2}$" <<<"${X}" && echo true
true
Or:
if grep -qE "^[^\+]{9}\+[^\+]{3}\+[^\+]{1}\+[^\+]{2}$" <<<"${line}"
then
exit 1
fi
You may also prefer to use a construct like below for handling files:
while read line; do
echo "${line}";
done < "${file}"
I'm reading a file in bash, line by line. I need to print lines that have the following format:
don't care <<< at least one character >>> don't care.
These are all the way which I have tried and none of them work:
if [[ $line =~ .*<<<.+>>>.* ]]; then
echo "$line"
fi
This has incorrect syntax
These two have correct syntax don't work
if [[ $line =~ '.*<<<.+>>>.*' ]]; then
echo "$line"
fi
And this:
if [[ $line == '*<<<*>>>*' ]]; then
echo "$line"
fi
So how to I tell bash to only print lines with that format? PD: I have tested and printing all lines works just fine.
Don't need regular expression. filename patterns will work just fine:
if [[ $line == *"<<<"?*">>>"* ]]; then ...
* - match zero or more characters
? - match exactly one character
"<<<" and ">>>" - literal strings: The angle brackets need to be quoted so bash does not interpret them as a here-string redirection.
$ line=foobar
$ [[ $line == *"<<<"?*">>>"* ]] && echo y || echo n
n
$ line='foo<<<>>>bar'
$ [[ $line == *"<<<"?*">>>"* ]] && echo y || echo n
n
$ line='foo<<<x>>>bar'
$ [[ $line == *"<<<"?*">>>"* ]] && echo y || echo n
y
$ line='foo<<<xyz>>>bar'
$ [[ $line == *"<<<"?*">>>"* ]] && echo y || echo n
y
For maximum compatibility, it's always a good idea to define your regex pattern as a separate variable in single quotes, then use it unquoted. This works for me:
re='<<<.+>>>'
if [[ $line =~ $re ]]; then
echo "$line"
fi
I got rid of the redundant leading/trailing .*, by the way.
Of course, I'm assuming that you have a valid reason to process the file in native bash (if not, just use grep -E '<<<.+>>>' file)
<, <<, <<<, >, and >> are special in the shell and need quoting:
[[ $line =~ '<<<'.+'>>>' ]]
. and + shouldn't be quoted, though, to keep their special meaning.
You don't need the leading and trailing .* in =~ matching, but you need them (or their equivalents) in patterns:
[[ $line == *'<<<'?*'>>>'* ]]
It's faster to use grep to extract lines:
grep -E '<<<.+>>>' input-file
I don't even understand why you are reading the file line per line. I have just launched following command in the bash prompt and it's working fine:
grep "<<<<.+>>>>" test.txt
where test.txt contains following data:
<<<<>>>>
<<<<a>>>>
<<<<aa>>>>
The result of the command was:
<<<<a>>>>
<<<<aa>>>>
I have a value in a variable that may be absolute or relative url, and I need to check which one it is.
I have found that there's a =~ operator in [[, but I can't get it to work. What am I doing wrong?
url="http://test"
if [[ "$url" =~ "^http://" ]];
then echo "absolute.";
fi;
You need to use regex without quote:
url="http://test"
if [[ "$url" =~ ^http:// ]]; then
echo "absolute."
fi
This outputs `absolute. as regex needs to be without quote in newer BASH (after BASH v3.1)
Or avoid regex and use glob matching:
if [[ "$url" == "http://"* ]]; then
echo "absolute."
fi
Say I want to match the leading dot in a string ".a"
So I type
[[ ".a" =~ ^\. ]] && echo "ha"
ha
[[ "a" =~ ^\. ]] && echo "ha"
ha
Why am I getting the same result here?
You need to escape the dot it has meaning beyond just a period - it is a metacharacter in regex.
[[ "a" =~ ^\. ]] && echo "ha"
Make the change in the other example as well.
Check your bash version - you need 4.0 or higher I believe.
There's some compatibility issues with =~ between Bash versions after 3.0. The safest way to use =~ in Bash is to put the RE pattern in a var:
$ pat='^\.foo'
$ [[ .foo =~ $pat ]] && echo yes || echo no
yes
$ [[ foo =~ $pat ]] && echo yes || echo no
no
$
For more details, see E14 on the Bash FAQ page.
Probably it's because bash tries to treat "." as a \ character, like \n \r etc.
In order to tell \ & . as 2 separate characters, try
[[ "a" =~ ^\\. ]] && echo ha