Quick unix command to display specific lines in the middle of a file

Question

Trying to debug an issue with a server and my only log file is a 20GB log file  with no timestamps even  Why do people use System out println   as logging  In production     Using grep  I ve found an area of the file that I d like to take a look at  line 347340107   Other than doing something like  head - lt  LINENUM   10 gt  filename   tail -20        which would require head to read through the first 347 million lines of the log file  is there a quick and easy command that would dump lines 347340100 - 347340200  for example  to the console   update I totally forgot that grep can print the context around a match     this works well  Thanks

User · Answer

You can use the ex command  a standard Unix editor  part of Vim now   e g    display a single line  e g  2nd one    ex  2p -scq file txt   corresponding sed syntax  sed -n  2p  file txt range of lines  e g  2-5 lines    ex  2 5p -scq file txt   sed syntax  sed -n  2 5p  file txt from the given line till the end  e g  5th to the end of the file    ex  5 p -scq file txt   sed syntax  sed -n  2  p  file txt multiple line ranges  e g  2-4 and 6-8 lines    ex  2 4p  6 8p -scq file txt   sed syntax  sed -n  2 4p 6 8p  file txt   Above commands can be tested with the following test file   seq 1 20  gt  file txt     Explanation      or -c followed by the command - execute the  vi vim  command after file has been read  -s - silent mode  also uses current terminal as a default output  q followed by -c is the command to quit editor  add   to do force quit  e g  -scq

User · Answer

What about   tail -n  347340107 filename   head -n 100   I didn t test it  but I think that would work

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Use  x  cat -n  lt file gt    grep  lt match gt    awk   print  1      Here you will get the line number where the match occurred   Now you can use the following command to print 100 lines  awk -v var   x   NR gt  var  amp  amp  NR lt  var 100 print    lt file gt    or you can use  sed  as well  sed -n    x    x 100 p   lt file gt

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What about   tail -n  347340107 filename   head -n 100   I didn t test it  but I think that would work

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with GNU-grep you could just say   grep --context 10

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You could try this command    egrep -n      lt filename gt    egrep   lt line number gt

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You could try this command    egrep -n      lt filename gt    egrep   lt line number gt

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To display a line from a  lt textfile gt  by its  lt line  gt   just do this   perl -wne  print if        lt line  gt    lt textfile gt    If you want a more powerful way to show a range of lines with regular expressions -- I won t say why grep is a bad idea for doing this  it should be fairly obvious -- this simple expression will show you your range in a single pass which is what you want when dealing with  20GB text files   perl -wne  print if m  lt regex1 gt      m  lt regex2 gt     lt filename gt     tip  if your regex has   in it  use something like m  lt regex gt   instead   This would print out  lt filename gt  starting with the line that matches  lt regex1 gt  up until  and including  the line that matches  lt regex2 gt    It doesn t take a wizard to see how a few tweaks can make it even more powerful    Last thing  perl  since it is a mature language  has many hidden enhancements to favor speed and performance  With this in mind  it makes it the obvious choice for such an operation since it was originally developed for handling large log files  text  databases  etc

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No there isn t  files are not line-addressable   There is no constant-time way to find the start of line n in a text file  You must stream through the file and count newlines   Use the simplest fastest tool you have to do the job  To me  using head makes much more sense than grep  since the latter is way more complicated  I m not saying  grep is slow   it really isn t  but I would be surprised if it s faster than head for this case  That d be a bug in head  basically

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What about   tail -n  347340107 filename   head -n 100   I didn t test it  but I think that would work

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I found two other solutions if you know the line number but nothing else  no grep possible    Assuming you need lines 20 to 40   sed -n  20 40p 41q  file name   or   awk  FNR gt  20  amp  amp  FNR lt  40  file name

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I prefer just going into less and    typing 50  to goto halfway the file   43210G to go to line 43210  43210 to do the same    and stuff like that   Even better  hit v to start editing  in vim  of course    at that location  Now  note that vim has the same key bindings

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with GNU-grep you could just say   grep --context 10

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With sed -e  1 N d  M q  you ll print lines N 1 through M  This is probably a bit better then grep -C as it doesn t try to match lines to a pattern

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To display a line from a  lt textfile gt  by its  lt line  gt   just do this   perl -wne  print if        lt line  gt    lt textfile gt    If you want a more powerful way to show a range of lines with regular expressions -- I won t say why grep is a bad idea for doing this  it should be fairly obvious -- this simple expression will show you your range in a single pass which is what you want when dealing with  20GB text files   perl -wne  print if m  lt regex1 gt      m  lt regex2 gt     lt filename gt     tip  if your regex has   in it  use something like m  lt regex gt   instead   This would print out  lt filename gt  starting with the line that matches  lt regex1 gt  up until  and including  the line that matches  lt regex2 gt    It doesn t take a wizard to see how a few tweaks can make it even more powerful    Last thing  perl  since it is a mature language  has many hidden enhancements to favor speed and performance  With this in mind  it makes it the obvious choice for such an operation since it was originally developed for handling large log files  text  databases  etc

User · Answer

Easy with perl  If you want to get line 1  3 and 5 from a file  say  etc passwd   perl -e  while  lt  gt   if    l   1 3 5   print     lt   etc passwd

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If your line number is 100 to read   head -100 filename   tail -1

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Use  x  cat -n  lt file gt    grep  lt match gt    awk   print  1      Here you will get the line number where the match occurred   Now you can use the following command to print 100 lines  awk -v var   x   NR gt  var  amp  amp  NR lt  var 100 print    lt file gt    or you can use  sed  as well  sed -n    x    x 100 p   lt file gt

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No there isn t  files are not line-addressable   There is no constant-time way to find the start of line n in a text file  You must stream through the file and count newlines   Use the simplest fastest tool you have to do the job  To me  using head makes much more sense than grep  since the latter is way more complicated  I m not saying  grep is slow   it really isn t  but I would be surprised if it s faster than head for this case  That d be a bug in head  basically

User · Answer

print line number 52 sed -n  52p    method 1 sed  52 d    method 2 sed  52q d    method 3   efficient on large files    method 3 efficient on large files  fastest way to display specific lines

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I found two other solutions if you know the line number but nothing else  no grep possible    Assuming you need lines 20 to 40   sed -n  20 40p 41q  file name   or   awk  FNR gt  20  amp  amp  FNR lt  40  file name

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I found two other solutions if you know the line number but nothing else  no grep possible    Assuming you need lines 20 to 40   sed -n  20 40p 41q  file name   or   awk  FNR gt  20  amp  amp  FNR lt  40  file name

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If your line number is 100 to read   head -100 filename   tail -1

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I d first split the file into few smaller ones like this    split --lines 50000  path to large file  path to output file prefix   and then grep on the resulting files

User · Answer

You can use the ex command  a standard Unix editor  part of Vim now   e g    display a single line  e g  2nd one    ex  2p -scq file txt   corresponding sed syntax  sed -n  2p  file txt range of lines  e g  2-5 lines    ex  2 5p -scq file txt   sed syntax  sed -n  2 5p  file txt from the given line till the end  e g  5th to the end of the file    ex  5 p -scq file txt   sed syntax  sed -n  2  p  file txt multiple line ranges  e g  2-4 and 6-8 lines    ex  2 4p  6 8p -scq file txt   sed syntax  sed -n  2 4p 6 8p  file txt   Above commands can be tested with the following test file   seq 1 20  gt  file txt     Explanation      or -c followed by the command - execute the  vi vim  command after file has been read  -s - silent mode  also uses current terminal as a default output  q followed by -c is the command to quit editor  add   to do force quit  e g  -scq

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Building on Sklivvz  answer  here s a nice function one can put in a  bash aliases file   It is efficient on huge files when printing stuff from the front of the file   function middle         startidx  1     len  2     endidx     startidx  len       filename  3      awk  FNR gt    startidx   amp  amp  FNR lt    endidx    print NR       0    FNR gt   endidx    print   END HERE    exit     filename

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With sed -e  1 N d  M q  you ll print lines N 1 through M  This is probably a bit better then grep -C as it doesn t try to match lines to a pattern

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I found two other solutions if you know the line number but nothing else  no grep possible    Assuming you need lines 20 to 40   sed -n  20 40p 41q  file name   or   awk  FNR gt  20  amp  amp  FNR lt  40  file name

User · Answer

Building on Sklivvz  answer  here s a nice function one can put in a  bash aliases file   It is efficient on huge files when printing stuff from the front of the file   function middle         startidx  1     len  2     endidx     startidx  len       filename  3      awk  FNR gt    startidx   amp  amp  FNR lt    endidx    print NR       0    FNR gt   endidx    print   END HERE    exit     filename

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sed will need to read the data too to count the lines  The only way a shortcut would be possible would there to be context order in the file to operate on  For example if there were log lines prepended with a fixed width time date etc  you could use the look unix utility to binary search through the files for particular dates times

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Easy with perl  If you want to get line 1  3 and 5 from a file  say  etc passwd   perl -e  while  lt  gt   if    l   1 3 5   print     lt   etc passwd

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Get ack  Ubuntu Debian install     sudo apt-get install ack-grep   Then run     ack --lines  START- END filename   Example     ack --lines 10-20 filename   From   man ack   --lines NUM     Only print line NUM of each file  Multiple lines can be given with multiple --lines options or as a comma separated list  --lines 3 5 7   --lines 4-7 also works       The lines are always output in ascending order  no matter the order given on the command line

User · Answer

with GNU-grep you could just say   grep --context 10

User · Answer

No there isn t  files are not line-addressable   There is no constant-time way to find the start of line n in a text file  You must stream through the file and count newlines   Use the simplest fastest tool you have to do the job  To me  using head makes much more sense than grep  since the latter is way more complicated  I m not saying  grep is slow   it really isn t  but I would be surprised if it s faster than head for this case  That d be a bug in head  basically

User · Answer

I prefer just going into less and    typing 50  to goto halfway the file   43210G to go to line 43210  43210 to do the same    and stuff like that   Even better  hit v to start editing  in vim  of course    at that location  Now  note that vim has the same key bindings

User · Answer

Get ack  Ubuntu Debian install     sudo apt-get install ack-grep   Then run     ack --lines  START- END filename   Example     ack --lines 10-20 filename   From   man ack   --lines NUM     Only print line NUM of each file  Multiple lines can be given with multiple --lines options or as a comma separated list  --lines 3 5 7   --lines 4-7 also works       The lines are always output in ascending order  no matter the order given on the command line

User · Answer

with GNU-grep you could just say   grep --context 10

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I am surprised only one other answer  by Ramana Reddy  suggested to add line numbers to the output   The following searches for the required line number and colours the output   file FILE lineno LINENO wb  107   bf  30 1   rb  101   yb  103  cat -n   file      GREP COLORS  se   wb    bf  cx   wb    bf  ms   rb    bf  sl   yb    bf   grep --color -C 10      space        lineno    space

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With sed -e  1 N d  M q  you ll print lines N 1 through M  This is probably a bit better then grep -C as it doesn t try to match lines to a pattern

User · Answer

I am surprised only one other answer  by Ramana Reddy  suggested to add line numbers to the output   The following searches for the required line number and colours the output   file FILE lineno LINENO wb  107   bf  30 1   rb  101   yb  103  cat -n   file      GREP COLORS  se   wb    bf  cx   wb    bf  ms   rb    bf  sl   yb    bf   grep --color -C 10      space        lineno    space

User · Answer

I d first split the file into few smaller ones like this    split --lines 50000  path to large file  path to output file prefix   and then grep on the resulting files

User · Answer

No there isn t  files are not line-addressable   There is no constant-time way to find the start of line n in a text file  You must stream through the file and count newlines   Use the simplest fastest tool you have to do the job  To me  using head makes much more sense than grep  since the latter is way more complicated  I m not saying  grep is slow   it really isn t  but I would be surprised if it s faster than head for this case  That d be a bug in head  basically

User · Answer

What about   tail -n  347340107 filename   head -n 100   I didn t test it  but I think that would work

User · Answer

I d first split the file into few smaller ones like this    split --lines 50000  path to large file  path to output file prefix   and then grep on the resulting files

User · Answer

I d first split the file into few smaller ones like this    split --lines 50000  path to large file  path to output file prefix   and then grep on the resulting files

User · Answer

With sed -e  1 N d  M q  you ll print lines N 1 through M  This is probably a bit better then grep -C as it doesn t try to match lines to a pattern

User · Answer

sed will need to read the data too to count the lines  The only way a shortcut would be possible would there to be context order in the file to operate on  For example if there were log lines prepended with a fixed width time date etc  you could use the look unix utility to binary search through the files for particular dates times

User · Answer

print line number 52 sed -n  52p    method 1 sed  52 d    method 2 sed  52q d    method 3   efficient on large files    method 3 efficient on large files  fastest way to display specific lines

[linux] Quick unix command to display specific lines in the middle of a file?

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