• initialize and export a variable
export foo=value
 
• $* cut the arguments containing an IFS character
"$@" does not do it (but the double quotes must be used)

#> set now "is the" time

#> for i in "$@"; do echo "($i)"; done
(now)
(is the)
(time)

#> for i in "$*"; do echo "($i)"; done
(now is the time)

#> for i in $@; do echo "($i)"; done
(now)
(is)
(the)
(time)

#> for i in $*; do echo "($i)"; done
(now)
(is)
(the)
(time)
 

• get the last argument
ksh allows any index
eval last=\${$#}
let index="$# - 1"
eval secondlast=\${index}
sh only allow index < 10
last=`shift \`expr $# - 1\`; echo "$1"`
secondlast=`shift \`expr $# - 2\`; echo "$1"`

test

• the syntax [...] use test
• the syntax [[ ... ]] execute the test by the shell itself, hence a performance gain

• i=0
  while
  do
    ...
    i=$(($i+1))
  done
  

• test if a variable is numeric or not
if /bin/expr "$var" + 0 1>&- 2>&-
then
  # numeric
else
  # non numeric
endif
 
• get the status of a command at the begining of a pipe
status = `((command; echo $? 1>&3) | tee foo 3>&) 3>&1)
 
• filename wildcard
/usr/include/{.,*}/*.h
 
• avoid that Ctrl-D destroys the shell
set -o ignoreeof
 
• avoid to overwrite a file
set o noclobber
 
• to suspend a shell
suspend
to restart it, send a SIGCONT or use fg %1
 
• loop on the lines of a file
while read line
  do
    echo $line
  done < $file
or
cat $file | while read line
  do
    echo $line
  done
 
• retrieve the directory where is the executable
  #!/bin/sh
if [ $0 = `basename $0` ]
  then
    myfullname=`which $0`
  else
    myfullname=$0
  fi
mydir=`dirname $myfullname`
nawk -f $mydir/tfwSum.awk $*


• compute some result while letting the data go through the script (i.e. it acts has a noop filter)
  #!/bin/sh
exitcode=1
fifo=/tmp/myfifo$$
mkfifo $fifo
set -o monitor
tee $fifo &
result=`grep 'reportType="SubTestResult"' $fifo | sed 's/^.*result="\([^"]*\)".*$/\1/'`
[ "x$result" = "xpass" ] && exitcode=0
rm $fifo
exit $exitcode


Last update: March 9^th, 2005 - Laurent