I would like to capture special character from a line:
var=`echo "#this is comment" | grep "[^a-zA-Z0-9 \t]"`
echo $var
Expected Output: #
But getting: #this is comment
Can someone help me out.
It seems like you want something more like:
var=`echo "#this is comment" | sed 's/[^a-zA-Z0-9 \t]//g;'`
Using sed will replace the characters; using grep was only searching for the characters.
Edit: Note that the \t construct is not guaranteed to be portable to all systems or locales; I believe if your sed supports POSIX regular expressions, using [:space:] may work better. (thanks #ghoti!)
string="#this is comment"
var=$(echo "$string" | sed 's/[a-zA-Z0-9 ]//g')
echo "$var"
I've removed \t as it's not portable.
If you want to do this with awk, as your tag suggests, you can use something like:
var=$(echo "$string" | awk '{gsub(/[a-zA-Z0-9 ]/, "")} 1')
Note that these are probably not good ways to achieve whatever it is that you're trying to do. If you post more of your code, showing us some context, we can help you avoid an XY problem.
Of course, you can also do substitutions like this directly in bash, if you want.
var=${string//[A-Za-z0-9 ]}
You'll save CPU and time by avoiding the call to an extra program when you don't really need it.
sed can be used for this, but tr is a better choice:
echo "#this is comment" | tr -d 'a-zA-Z0-9 \t'
tr also supports character classes such as [:space:] and [:alpha:]
Related
I would like to print directly with sed a HEX value translation by isolating the HEX values in capture groups. This works:
echo bbb3Accc | sed -n 's/3A/\x3A/p'
bbb:ccc
...but this doesn't work:
echo bbb3Accc | sed 's/\(3A\)/\x\1/'
bbbx3Accc
...or an actual capture group REGEX matching based on URL encoded strings:
echo bbb%3Accc | sed 's/%\([A-Za-z0-9]\)/\x\1/'
bbbx3Accc
Apparently sed no longer interprets and translates the HEX value if it is constructed from a REGEX capture group, together with the \x escape.
But I am wondering if there's a workaround that I am not aware of, to make this work only with sed. Note that I am aware that I can do a bash command substitution and wrap the sed syntax in a echo -e but I would like to avoid that.
Your question isn't clear but maybe this is what you're trying to do using GNU awk for multi-char RS, RT, and strtonum():
$ echo 'bbb%3Accc%21ddd' |
gawk -v RS='%[[:xdigit:]]{2}' 'sub(/%/,"0x",RT){RT=sprintf("%c",strtonum(RT))} {ORS=RT} 1'
bbb:ccc!ddd
As mentioned in the comments, \xAB is interpreted by sed's parser, rather than as an expression, so \x won't work in the way you were trying.
sed is pretty primitive and your example is beyond what it is intended for, so you'd be better off using something more general purpose. For example, in Perl:
$ echo bbb3Accc | perl -ple 's/([0-9A-F]{2})/chr(hex($1))/ge'
bbb:ccc
I want to extract a number of variable length from a string.
The string looks like this:
used_memory:1775220696
I would like to have the 1775220696 part in a variable. There are a lot of questions about this, but I could not find a solution that suits my needs.
You can use cut:
my_val=$(echo "used_memory:1775220696" | cut -d':' -f2)
Or also awk:
my_val=$(echo "used_memory:1775220696" | awk -F':' '{print $2}')
Use parameter expansion:
string=used_memory:1775220696
num=${string#*:} # Delete everything up to the first colon.
I used to use egrep
echo used_memory:1775220696 | egrep -o [0-9]+
Output:
1775220696
use the regex:
s/^[^:]*://g
you use it with sed or perl and get the part you needed.
> echo "used_memory:1775220696" | perl -pe 's/^[^:]*://g'
1775220696
bash supports regular-expression matching, but for a simple case like this it is overkill; use parameter expansion (see choroba's answer).
For the sake of completeness, here's an example using regular expression matching:
[[ $string =~ (.*):([[:digit:]]+) ]] && num=${BASH_REMATCH[2]}
Can be done using awk, like this:
var=`echo "used_memory:1775220696" | awk -F':' '{print $2;}'`
echo $var
output:
1775220696
If your number could be anywhere in the string, but you know that the digits are contiguous, you can use shell parameter expansion to remove everything that is not a digit:
$ str=used_memory:1775220696
$ num=${str//[!0-9]}
$ echo "$num"
1775220696
This works also for used_memory:1775220696andmoretext and 123numberfirst. However, something like abc123def456 would become 123456.
echo ddayaynightday | sed 's/day//g'
It ends up daynight
Is there anyway to make it substitute until no more match ?
My preferred form, for this case:
echo ddayaynightday | sed -e ':loop' -e 's/day//g' -e 't loop'
This is the same as everyone else's, except that it uses multiple -e commands to make the three lines and uses the t construct—which means "branch if you did a successful substitution"—to iterate.
This might work for you:
echo ddayaynightday | sed ':a;s/day//g;ta'
night
The g flag deliberately doesn't re-match against the substituted portion of the string. What you'll need to do is a bit different. Try this:
echo ddayaynightday | sed $':begin\n/day/{ s///; bbegin\n}'
Due to BSD Sed's quirkiness the embedded newlines are required. If you're using GNU Sed you may be able to get away with
sed ':begin;/day/{ s///; bbegin }'
with bash:
str=ddayaynightday
while true; do tmp=${str//day/}; [[ $tmp = $str ]] && break; str=$tmp; done
echo $str
The following works:
$ echo ddayaynightday | sed ':loop;/day/{s///g;b loop}'
night
Depending on your system, the ; may not work to separate commands, so you can use the following instead:
echo ddayaynightday | sed -e ':loop' -e '/day/{s///g
b loop}'
Explanation:
:loop # Create the label 'loop'
/day/{ # if the pattern space matches 'day'
s///g # remove all occurrence of 'day' from the pattern space
b loop # go back to the label 'loop'
}
If the b loop portion of the command is not executed, the current contents of the pattern space are printed and the next line is read.
Ok, here they're: while and strlen in bash.
Using them one may implement my idea:
Repeat until its length will stop changing.
There's neither way to set flag nor way to write such regex, to "substitute until no more match".
In my bash script, I have an array of filenames like
files=( "site_hello.xml" "site_test.xml" "site_live.xml" )
I need to extract the characters between the underscore and the .xml extension so that I can loop through them for use in a function.
If this were python, I might use something like
re.match("site_(.*)\.xml")
and then extract the first matched group.
Unfortunately this project needs to be in bash, so -- How can I do this kind of thing in a bash script? I'm not very good with grep or sed or awk.
Something like the following should work
files2=(${files[#]#site_}) #Strip the leading site_ from each element
files3=(${files2[#]%.xml}) #Strip the trailing .xml
EDIT: After correcting those two typos, it does seem to work :)
xbraer#NO01601 ~
$ VAR=`echo "site_hello.xml" | sed -e 's/.*_\(.*\)\.xml/\1/g'`
xbraer#NO01601 ~
$ echo $VAR
hello
xbraer#NO01601 ~
$
Does this answer your question?
Just run the variables through sed in backticks (``)
I don't remember the array syntax in bash, but I guess you know that well enough yourself, if you're programming bash ;)
If it's unclear, dont hesitate to ask again. :)
I'd use cut to split the string.
for i in site_hello.xml site_test.xml site_live.xml; do echo $i | cut -d'.' -f1 | cut -d'_' -f2; done
This can also be done in awk:
for i in site_hello.xml site_test.xml site_live.xml; do echo $i | awk -F'.' '{print $1}' | awk -F'_' '{print $2}'; done
If you're using arrays, you probably should not be using bash.
A more appropriate example wold be
ls site_*.xml | sed 's/^site_//' | sed 's/\.xml$//'
This produces output consisting of the parts you wanted. Backtick or redirect as needed.
I'm dealing with a specific filenames, and need to extract information from them.
The structure of the filename is similar to: "20100613_M4_28007834.005_F_RANDOMSTR.raw.gz"
with RANDOMSTR a string of max 22 chars, and which may contain a substring (or not) with the format "-W[0-9].[0-9]{2}.[0-9]{3}". This substring also has the unique feature of starting with "-W".
The information I need to extract is the substring of RANDOMSTR without this optional substring.
I want to implement this in a bash script, and so far the best option I found is to use gawk with a regular expression. My best attempt so far fails:
gawk --re-interval '{match ($0,"([0-9]{8})_(M[0-9])_([0-9]{8}\\.[0-9]{3})_(.)_(.*)(-W.*)?.raw.gz",arr); print arr[5]}' <<< "20100613_M4_28007834.005_F_OTHER-STRING-W0.40+045.raw.gz"
OTHER-STRING-W0.40+045
The expected results are:
gawk --re-interval '{match ($0,$regexp,arr); print arr[5]}' <<< "20100613_M4_28007834.005_F_SOME-STRING.raw.gz"
SOME-STRING
gawk --re-interval '{match ($0,$regexp,arr); print arr[5]}' <<< "20100613_M4_28007834.005_F_OTHER-STRING-W0.40+045.raw.gz"
OTHER-STRING
How can I get the desired effect.
Thanks.
You need to be able to use look-arounds and I don't think awk/gawk supports that, but grep -P does.
$ pat='(?<=[0-9]{8}_M[0-9]_[0-9]{8}\.[0-9]{3}_._)(.*?)(?=(-W.*)?\.raw\.gz)'
$ echo "20100613_M4_28007834.005_F_SOME-STRING.raw.gz" | grep -Po "$pat"
SOME-STRING
$ echo "20100613_M4_28007834.005_F_OTHER-STRING-W0.40+045.raw.gz" | grep -Po "$pat"
OTHER-STRING
While the grep solution is very nice indeed, the OP didn't mention an operating system, and the -P option only seems to be available in Linux. It's also pretty simple to do this in awk.
$ awk -F_ '{sub(/(-W[0-9].[0-9]+.[0-9]+)?\.raw\.gz$/,"",$NF); print $NF}' <<EOT
> 20100613_M4_28007834.005_F_SOME-STRING.raw.gz
> 20100613_M4_28007834.005_F_OTHER-STRING-W0.40+045.raw.gz
> EOT
SOME-STRING
OTHER-STRING
$
Note that this breaks on "20100613_M4_28007834.005_F_OTHER-STRING-W0_40+045.raw.gz". If this is a risk, and -W only shows up in the place shown above, it might be better to use something like:
$ awk -F_ '{sub(/(-W[0-9.+]+)?\.raw\.gz$/,"",$NF); print $NF}'
The difficulty here seems to be the fact that the (.*) before the optional (-W.*)? gobbles up the latter text. Using a non-greedy match doesn't help either. My regex-fu is unfortunately too weak to combat this.
If you don't mind a multi-pass solution, then a simpler approach would be to first sanitise the input by removing the trailing .raw.gz and possible -W*.
str="20100613_M4_28007834.005_F_OTHER-STRING-W0.40+045.raw.gz"
echo ${str%.raw.gz} | # remove trailing .raw.gz
sed 's/-W.*$//' | # remove trainling -W.*, if any
sed -nr 's/[0-9]{8}_M[0-9]_[0-9]{8}\.[0-9]{3}_._(.*)/\1/p'
I used sed, but you can just as well use gawk/awk.
Wasn't able to get reluctant quantifiers going, but running through two regexes in sequence does the job:
sed -E -e 's/^.{27}(.*).raw.gz$/\1/' << FOO | sed -E -e 's/-W[0-9.]+\+[0-9.]+$//'
20100613_M4_28007834.005_F_SOME-STRING.raw.gz
20100613_M4_28007834.005_F_OTHER-STRING-W0.40+045.raw.gz
FOO