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Question

sed + regular expression: how to get everything before a given character

Answer 1

+2 A:

sed -ne "s/^myhome=//p"

Answering to your comment below:

sed -ne "s/^[^=]\+=//p"

Antony Hatchkins 2010-01-14 11:25:35

thanks! But is there a way of having a more generic expression where 'myhome' is not used, i.e. remove everything that before the '=' regardless of what is before '='

DavidM 2010-01-14 11:29:14

updated the answer

Antony Hatchkins 2010-01-14 11:31:30

actually, I just tried "s/^[^=]+=//p" and it doesn't work... it returns nothing (with -ne) or everything with (-e)

DavidM 2010-01-14 11:34:51

Just tried this: ``echo "myhome=foo" | sed -ne 's/^[^=]*=//p'`` and taht results in "foo" being written on stdout. So, rplace the + with a * and all SHOULD be well.

Vatine 2010-01-14 11:45:36

fixed, plus should be escaped in sed regexp. plus suggests that line `=foo` should be left as is. `*` works too.

Antony Hatchkins 2010-01-14 12:57:22

Answer 2

+1 A:

sed 's+.*=++g'

should do the job.

2010-01-14 11:26:43

great, exactly what I wanted

DavidM 2010-01-14 11:31:12

Beware: if the RHS contains a `=` this will not work.

2010-01-14 11:32:50

yes, thanks luts, good to know.

DavidM 2010-01-14 11:37:40

myhome=/home/username=john will be truncated to john

Antony Hatchkins 2010-01-14 13:00:07

also empty lines and lines without `=` will be printed

Antony Hatchkins 2010-01-14 13:00:48

Answer 3

+1 A:

use awk

awk -F"=" '{print $2}' file
awk '{sub(/^.[^=]*=/,"")}1' file

or just use the shell

while IFS="="  read -r a b
do
    echo $b
done <"file"

for sed, try this

sed -ne "s/^.[^=]*=//p" file

just shell string manipulation

$ myhome=/home/username=blah
$ echo ${myhome%%=}
/home/username=blah

ghostdog74 2010-01-14 11:28:30

thanks, I know awk better and thought of doing it just like you suggested, but I was trying to force myself to use/learn sed :-)

DavidM 2010-01-14 11:33:24

if you know awk, there is no need to know sed. the fundamentals of sed is regex. When you learn awk, you also learn regex.

ghostdog74 2010-01-14 11:34:36

I would argue that there is always a need to learn other tools... one day, you might have to deal with a project which uses sed only...and then you're stuffed

DavidM 2010-01-14 11:36:03

@dmichel: True, see http://memory-alpha.org/en/wiki/Arena_(episode)

Dennis Williamson 2010-01-14 16:51:10

Answer 4

+1 A:

sed can do the greping for you, too.

$ sed -n -e "s/^myhome=//p" property

The -n is:

suppress automatic printing of pattern space

While the trailing p prints a matched line.

2010-01-14 11:29:22

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sed + regular expression: how to get everything before a given character

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