revposparams.sh

Shall高级编程

#!/bin/bash
# revposparams.sh: Reverse positional parameters.
# Script by Dan Jacobson, with stylistic revisions by document author.


set a\ b c d\ e;
#     ^      ^     Spaces escaped 
#       ^ ^        Spaces not escaped
OIFS=$IFS; IFS=:;
#              ^   Saving old IFS and setting new one.

echo

until [ $# -eq 0 ]
do          #      Step through positional parameters.
  echo "### k0 = "$k""     # Before
  k=$1:$k;  #      Append each pos param to loop variable.
#     ^
  echo "### k = "$k""      # After
  echo
  shift;
done

set $k  #  Set new positional parameters.
echo -
echo $# #  Count of positional parameters.
echo -
echo

for i   #  Omitting the "in list" sets the variable -- i --
        #+ to the positional parameters.
do
  echo $i  # Display new positional parameters.
done

IFS=$OIFS  # Restore IFS.

#  Question:
#  Is it necessary to set an new IFS, internal field separator,
#+ in order for this script to work properly?
#  What happens if you don't? Try it.
#  And, why use the new IFS -- a colon -- in line 17,
#+ to append to the loop variable?
#  What is the purpose of this?

exit 0

$ ./revposparams.sh

### k0 = 
### k = a b

### k0 = a b
### k = c a b

### k0 = c a b
### k = d e c a b

-
3
-

d e
c
a b