More about Shell Script

1
Lecture 6

• More about Shell Script

2
Review Shell Variables

• Special shell variables
• Name Description
• (For passing parameters)
• 1 - 9 the positional parameters. (shiftn1
  becomes n handling more than 9 parameters)
• 0 the name of the command that is being
  executed
• the number of positional arguments
• (for process control)
• ? the exit status of the last command executed
• the process number of this shell
• ! the process id of the command run in the
  background.

3
Example 4

• Task Write a script that accepts an optional
  command line parameter a directory name and
  prints the file system structure under this
  directory in the form of a tree. W/o parameters,
  it should start in the current directory. Call
  this script dirtree.csh

4
Example Result of dirtree.csh

• dirtree
• ------bin
• ------.garbage
• ------file1
• ------examples
• ------arg
• ------average.csh
• ------fileinfo.csh
• ------hw6.sh
• ------lab3

5
Script dirtree.csh

• !/bin/csh -f
• start at current dir, if no param.
• if(argv 0) then
• set thisdir"."
• else
• set thisdirargv1
• endif
• if(?TREEPREFIX) then
• set prefix"TREEPREFIX"
• else
• set prefix""
• endif
• echo "prefix"
• set filelistls -A thisdir

• foreach file (filelist)
• echo "prefix------file"
• if(-d "thisdir/file") then
• if(file filelistfilelist) then
• setenv TREEPREFIX
• "prefix "
• else
• setenv TREEPREFIX
• "prefix "
• endif
• one level down the recursion ladder
• 0 "thisdir/file"
• endif
• end
• echo "prefix"

6
Example 5 watchfile.csh

• Task write a script that watches a file with du.
  perhaps useful if you have a slow internet
  connection and want to track the progress of a
  large download. Won't stop until you press C!
• Usage is watchfile filename delay_interval
• if delay_interval is not specified, the script
  pauses 5 seconds between each time it shows the
  file size and elapsed time.

7
Example result of watchfile.csh

• ./watchfile.csh fileinfo.csh 2
• watching the file fileinfo.csh
• Starting time 213721
• 2 seconds FILE fileinfo.csh SIZE 1 Kbytes
• 4 seconds FILE fileinfo.csh SIZE 1 Kbytes
• 6 seconds FILE fileinfo.csh SIZE 1 Kbytes
• 8 seconds FILE fileinfo.csh SIZE 1 Kbytes
• 10 seconds FILE fileinfo.csh SIZE 1 Kbytes
• 12 seconds FILE fileinfo.csh SIZE 1 Kbytes
• 14 seconds FILE fileinfo.csh SIZE 1 Kbytes
• C

8
Script watchfile.csh

• !/bin/csh -f
• make sure there is at least 1 command line
  parameter
• if ( argv 0 ) then
• echo "usage watchfile filename
  delay_interval"
• exit
• else
• record the file name we are supposed to
  watch
• set file1
• endif
• make sure it is really a file
• if (! -f file ) then
• echo "Error file does not exist or is not a
  file!"
• exit
• endif

• this variable is the time we wait between
  printing the file size
• (in seconds)
• if ( 2 ) then
• we got 2 parameters, use the second as the
  delay interval
• set delay2
• else
• set delay5
• endif
• get the initial hour, min and second
• set ihourdate H
• set imindate M
• set isecdate S

9
Script watchfile.csh(II)

• while ( 1 )
• _at_ ikbytes dkbytes
• sleep delay
• get the current hour, min and second
• _at_ hourdate H
• _at_ mindate M
• _at_ secdate S
• compute elapsed time
• _at_ dhour hour - ihour
• _at_ dminmin - imin
• _at_ dsecsec - isec
• _at_ kbytesdu -L -k file cut -f1
• _at_ dkbytes kbytes - ikbytes
• if (dkbytes gt 1) then
• _at_ elapsed dhour 3600 dmin 60
  dsec
• echo -n "elapsed seconds "
• echo " FILE " file " SIZE " kbytes
  "Kbytes"
• else
• exit

• set hour 0
• set min 0
• set sec 0
• compute elapsed time
• set dhour 0
• set dmin 0
• set dsec 0
• set elapsed 0
• set ikbytes du -L -k file cut -f1
• set kbytes ikbytes
• set dkbytes 0
• echo "watching the file 1"
• echo "Starting time ihouriminisec"
• now go in to a loop that never
• ends, except the size is not