Shell Programming and Scripting

Hello,

I am using sed command to place a comma dynamically in certain positions. When the position variable exceeds 255 characters, it errors out. I would appreciate if someone can point in the correct direction

Code:

sed 's/^\(.\{'"$pos"'\}\)./\1,/' ragha.txt > ragha3.txt

If $pos > 255, it errors out with cannot parse.

Care to tell us which OS (to be precise: which sed) you use?

bakunin

Use perl:

Code:

pos=390
perl -pe 's/^(.{'"$pos"'})./$1,/' ragha.txt

Hi Bakunin,

We are using HP -UX Operating System.

MadiinGermany.. Unfortunately perl is not installed in our system.

Thanks,
Ragha

Try with awk

Code:

awk -v pos=390 '{print substr($0,1,pos) "," substr($0,pos+1)}' ragha.txt

The limitation is common to all "regular" sed variants, AIX-sed and Solaris-sed do the same. It is not possible to use ranges bigger than 255 constructs with curly braces ("\{xx\}"). Maybe Don Cragun can shed more light on what the standards prescribe on the behavior of sed.

One possbility is to use two such ranges, like this:

Code:

sed 's/^.\{255\}.\{25\}//' file

but i have to admit this is cumbersome and a workaround at best, certainly not a solution. Other than using one of the other text filters (perl, awk, ... like MadeInGermany suggested) there is maybe GNU-sed, which might not have the limitation. Alas i don't know for sure, you will have to try that out on the next Linux system you find lying around.

I hope this helps.

bakunin

To replace the 391st character I think that would be:

Code:

sed 's/^\(.\{255\}.\{135\}\)./\1,/' file

The standards say that systems must allow RE_DUP_MAX repeated occurrences of a BRE or ERE in an interval expression and that RE_DUP_MAX but be at least _POSIX_RE_DUP_MAX which is defined by the current standards to be 255. (This is for all BREs and EREs; not just BREs used in sed.) You can find the values of RE_DUP_MAX and _POSIX_RE_DUP_MAX on your system with:

Code:

getconf _POSIX_RE_DUP_MAX;getconf RE_DUP_MAX

If the awk suggestion provided by MadeInGermany in post #5 in this thread is not acceptable, one could write a shell function to generate the BRE to be used by sed when given $pos as an operand changing:

Code:

sed 's/^\(.\{'"$pos"'\}\)./\1,/' ragha.txt > ragha3.txt

to:

Code:

sed 's/^\('"$(func_name "$pos")"'\)./\1,/' raga.txt > ragha3.txt

to get a BRE using as many interval expressions as are needed (remembering, of course, that sed also has a maximum line length limit (LINE_MAX)).