Substring from end to a letter's index length in unix shell script

Question

I have string say,

a="abc_def ghi__333_31122013_Monthly.pdf"

I need the substract monthly and 31122013 from the above string in shell script. Basically doing substring from last till the first index of '_'.

Any help or suggestion is welcome.

Navdeep

Possible duplicate of [this](http://stackoverflow.com/questions/428109/extract-substring-in-bash) — Anubhab, Dec 31 '13 at 08:25
"Subtract" as in "substitute with nothing"? Or do you mean "extract"? — tripleee, Dec 31 '13 at 08:31
Are these completely static strings, or do you have a pattern like "last sequence of eight digits between underscores"? — tripleee, Dec 31 '13 at 08:32

score 2 · Accepted Answer · answered Dec 31 '13 at 08:26

2

Using awk:

a="abc_def ghi__333_31122013_Monthly.pdf"
awk -F '[_.]' '{print $(NF-2), $(NF-1)}' <<< "$a"
31122013 Monthly

Using IFS in BASH:

IFS=[_.] && arr=($a)
l=${#arr[@]}
echo ${arr[$l-3]}
31122013
echo ${arr[$l-2]}
Monthly

answered Dec 31 '13 at 08:26

anubhava

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Innovative answer..super like :) – Anubhab Dec 31 '13 at 08:28

janos · Answer 2 · 2013-12-31T08:36:01.053

If you want to remove _31122013_Monthly, where 31122013 is variable, you could use a substitution like this:

$ a="abc_def ghi__333_31122013_Monthly.pdf"
$ echo ${a/_????????_Monthly}
abc_def ghi__333.pdf

If on the other hand you really want this:

Basically doing substring from last till the first index of '_'.

then, you could do this:

$ echo ${a/_*_}
abcMonthly.pdf

Or if you want to cut off until the _ right before 31122013_Monthly.pdf then you can:

$ echo ${a#*__*_}
31122013_Monthly.pdf

score 0 · Answer 3 · answered Dec 31 '13 at 08:37

If you actually want to remove the last sequence of eight digits between underscores and the following alphabetic token up until just before the full stop, try something like

ext=${a##*.}
echo ${a%_[0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9]_*}.$ext

(This isn't entirely precise; it will replace the tail from the eight digits with underscores with nothing, then tack the extension back on.)

Substring from end to a letter's index length in unix shell script

3 Answers3