The exec builtin command

exec [-a NAME] [-cl] [COMMAND] [ARG...] [REDIRECTION...]

The exec builtin command is used to

• replace the shell with a given program (executing it, not as new process)
• set redirections for the program to execute or for the current shell

If only redirections are given, the redirections affect the current shell without executing any program.

• on redirection errors it returns 1, otherwise 0
• on exec failures:
  • a non-interactive shell terminates; if the shell option execfail is set exec returns failure
  • in an interactive shell, exec returns failure

myprog=/bin/ls
echo "This is the wrapper script, it will exec $myprog"
 
# do some vodoo here, probably change the arguments etc.
# well, stuff a wrapper is there for
 
exec "$myprog" "$@"

# open it
exec 3< input.txt
 
# for example: read one line from the file(-descriptor)
read -u 3 LINE
# or
read LINE <&3
 
# finally, close it
exec 3<&-

To redirect the whole stdout and stderr of the shell or shellscript to a file, you can use the exec builtin command:

exec >/var/adm/my.log 2>&1
 
# script continues here...

• POSIX® specifies error code ranges:
  • if exec can't find the program to execute, the error code shall be 126
  • on a redirection error, the error code shall be between 1 and 125
• the -a NAME option appeared in Bash 4.2-alpha
• POSIX® does not specify any options for exec (like -c, -l, -a NAME).

• Redirection