sed pattern parts as input for other bash function

Question

I'm trying to replace floating-point numbers like 1.2e + 3 with their integer value 1200. For this I use sed in the following way:

 echo '"1.2e+04"' | sed "s/\"\([0-9]\+\.[0-9]\+\)e+\([0-9]\+\)\"/$(echo \1*10^\2|bc -l)/"

but the pattern parts \1 and \2 doesn't get evaluated in the echo.

Is there a way to solve this problem with sed? Thanks in advance

See [How to get bc to handle numbers in scientific (aka exponential) notation?](https://stackoverflow.com/questions/12882611/how-to-get-bc-to-handle-numbers-in-scientific-aka-exponential-notation) — Wiktor Stribiżew, Jan 16 '19 at 11:33

score 1 · Answer 1 · answered Jan 16 '19 at 12:43

1

If you are happy with awk command like this can do the work:

echo 1.2e+4|awk '{printf "%d",$0}'

answered Jan 16 '19 at 12:43

Romeo Ninov

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score 1 · Accepted Answer · answered Jan 16 '19 at 13:02

Within the double quotes, \1 and \2 are interpreted as literal 1 and 2. You need to put additional backslashes to escape them. In addition, $(command substitution) in sed replacement seems not to work when combined with back references. If you are using GNU sed, you can instead say something like:

echo '"1.2e+04"' | sed "s/\"\([0-9]\+\.[0-9]\+\)e+\([0-9]\+\)\"/echo \"\\1*10^\\2\"|bc -l/;e"

which yields:

12000.0

If you want to chop off the decimal point, you'll know what to do ;-).

user7440787 · Answer 3 · 2019-01-16T13:26:08.920

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It is perhaps better to use perl (or other typed language) to manage the variable types:

echo '"1.2e+04"' | perl -lane 'my $a=$_;$a=~ s/"//g;print sprintf("%.10g",$a);print $a;'

~~In any case, your sed expression is incorrect, it should be:~~

~~echo '"1.2e+04"' | sed "s/\"$[0-9]\+\.[0-9]\+$e+$[0-9]\+$\"/$(echo \1*10^\3 + \2*10^$(echo \3 - 1 | bc -l)|bc -l)/"~~

edited Jan 16 '19 at 13:26

answered Jan 16 '19 at 11:12

user7440787

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how you are getting the value for `\3` in `sed` command, also i believe the output of your `sed` command should be `12000` instead of `1200` . – User123 Jan 16 '19 at 11:30

Mauri · Answer 4 · 2019-01-17T00:39:34.953

The best way to solve the problem properly is to use an advanced combination of @ tshiono and @ Romeo solutions:

sed "s/\(.*\)\([0-9]\+\.[0-9]\+e+[0-9]\+\)\(.*\)/printf '\1'\; echo \2 |awk '{printf \"%d\",\$0}'\;printf '\3'\;/e"

So it is possible to convert all such floats into arbitrary contexts.

for example:

echo '"1.2e+04"' | sed "s/\(.*\)\([0-9]\+\.[0-9]\+e+[0-9]\+\)\(.*\)/printf '\1'\; echo \2 |awk '{printf \"%d\",\$0}'\;printf '\3'\;/e"

outputs

"12000"

and

echo 'abc"1.2e+04"def' | sed "s/\(.*\)\([0-9]\+\.[0-9]\+e+[0-9]\+\)\(.*\)/printf '\1'\; echo \2 |awk '{printf \"%d\",\$0}'\;printf '\3'\;/e"

outputs

abc"12000"def

sed pattern parts as input for other bash function

4 Answers4