Trim last 3 characters of a line WITHOUT using sed or perl etc

Question

I ve got a shell script outputting data like this   1234567890    1234567891      I need to remove JUST the last three characters        I know I can do it via   whatever    sed  s            1     But I DON T want to use sed for speed purposes  It will always be the same last 3 characters   Any quick way of cleaning up the output

User · Answer

Another answer relies on the third-to-last character being a space. This will work with (almost) any character in that position and does it "WITHOUT using sed, or perl, etc.":

while read -r line
do
    echo ${line:0:${#line}-3}
done

If your lines are fixed length change the echo to:

echo ${line:0:9}

or

printf "%.10s\n" "$line"

but each of these is definitely much slower than sed.

User · Answer

No need for cut or magic  in bash you can cut a string like so     ORGSTRING  123456    CUTSTRING   ORGSTRING 0 -3    echo  The original string   ORGSTRING    echo  The new  shorter and faster string   CUTSTRING    See http   tldp org LDP abs html string-manipulation html

User · Answer

You can use awk just to print the first  field  if there won t be any spaces  or if there will be  change the separator    I put the fields you had above into a file and did this  awk    print  1     lt  test txt  1234567890 1234567891   I don t know if that s any better

User · Answer

If the script always outputs lines of 10 characters followed by 3 extra  in other words  you just want the first 10 characters   you can use  script   cut -c 1-10   If it outputs an uncertain number of non-space characters  followed by a space and then 2 other extra characters  in other words  you just want the first field   you can use  script   cut -d     -f 1       as in majhool s comment earlier   Depending on your platform  you may also have colrm  which  again  would work if the lines are a fixed length   script   colrm 11

User · Answer

what do you mean don t want to use sed awk for speed purposes  sed awk are faster than the shell s while read loop for processing files     sed  s    t         file 1234567890 1234567891    sed  s          file 1234567890 1234567891   with bash shell  while read -r a b do  echo  a done  lt file

User · Answer

I can guarantee you that bash alone won t be any faster than sed for this task   Starting up external processes in bash is a generally bad idea but only if you do it a lot   So  if you re starting a sed process for each line of your input  I d be concerned  But you re not  You only need to start one sed which will do all the work for you   You may however find that the following sed will be a bit faster than your version    whatever    sed  s           All this does is remove the last three characters on each line  rather than substituting the whole line with a shorter version of itself  Now maybe more modern RE engines can optimise your command but why take the risk   To be honest  about the only way I can think of that would be faster would be to hand-craft your own C-based filter program  And the only reason that may be faster than sed is because you can take advantage of the extra knowledge you have on your processing needs  sed has to allow for generalised procession so may be slower because of that    Don t forget the optimisation mantra   Measure  don t guess      If you really want to do this one line at a time in bash  and I still maintain that it s a bad idea   you can use   pax gt  line 123456789abc pax gt  line2   line       pax gt  echo   line2  123456789 pax gt        You may also want to investigate whether you actually need a speed improvement  If you process the lines as one big chunk  you ll see that sed is plenty fast  Type in the following      usr bin bash  echo This is a pretty chunky line with three bad characters at the end XXX  gt qq1 for i in 4 16 64 256 1024 4096 16384 65536   do     cat qq1 qq1  gt qq2     cat qq2 qq2  gt qq1 done  head -20000l qq1  gt qq2 wc -l qq2  date time sed  s         qq2  gt qq1 date head -3l qq1   and run it  Here s the output on my  not very fast at all  R40 laptop   pax gt    chk sh 20000 qq2 Sat Jul 24 13 09 15 WAST 2010  real    0m0 851s user    0m0 781s sys     0m0 050s Sat Jul 24 13 09 16 WAST 2010 This is a pretty chunky line with three bad characters at the end  This is a pretty chunky line with three bad characters at the end  This is a pretty chunky line with three bad characters at the end    That s 20 000 lines in under a second  pretty good for something that s only done every hour

User · Answer

You could try    whatever    while read line  do echo  line   head --bytes -3  done    head itself should be faster than sed or cut because there s no regex or delimeter matching  but invoking a for every line separately would probably outweigh that

User · Answer

Here s an old-fashioned unix trick for removing the last 3 characters from a line that makes no use of sed OR awk      gt  echo 987654321   rev   cut -c 4-   rev  987654   Unlike the earlier example using  cut   this does not require knowledge of the line length

User · Answer

Assuming all data is formatted like your example  use  cut  to get the first column only     cat  file   cut -d     -f 1     or to get the first 10 chars   cat  file   cut -c 1-10

User · Answer

x  can haz    echo    x       can

User · Answer

Both awk and sed are plenty fast  but if you think it matters feel free to use one of the following   If the characters that you want to delete are always at the end of the string  echo  1234567890       tr -d        If they can appear anywhere within the string and you only want to delete those at the end  echo  1234567890       rev   cut -c 4-   rev   The man pages of all the commands will explain what s going on   I think you should use sed  though

User · Answer

Note  This answer is somewhat intended to be a joke  but it actually does work        bin bash outfile   tmp  RANDOM  cfile   outfile c  echo   include  lt stdio h gt  int main void  int e 1 char c while  c getc stdin    -1  if c  10 e 1 if c  32 e 0 if e putc c stdout       gt  gt    cfile  gcc -o   outfile    cfile  rm   cfile  cat somedata txt     outfile  rm   outfile    You can replace cat somedata txt with a different command

[unix] Trim last 3 characters of a line WITHOUT using sed, or perl, etc

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