Simple Bash Scripts

• Example Scripts are found in the /home/cccc/src directory. We will copy them as needed.
• examples that run your machine : /etc/rcS.d/*.sh
• variables See examples in the variables directory.
  1. $ indicates a variable. See hello.sh
  2. $#, $?, $0, $*, $@ are built into the bash. # of arguments, ? last exit value, 0 name of shell program, * all arguments, @ all in quotes.
  3. Environment variables. (Note the caps)
     • run env to see them.
     • $LOGNAME
     • $HOME
     • $USER
     • $PWD
     • set them in bash.profile, bash.rc or your script.
  4. Local variables are seen only in a function and do not affect variables by the same name outside the function. See local.sh
• Redirection and Pipes
  1. ">" is output redirection to a file.
  2. "<", input redirection is useful for commands that don't take a file.
  3. The standard file descriptors, stdin, stdout, stderr are referenced like pointers for redirection.
     • "ls -l > ls_l.txt" puts list into a file.
     • "grep da * 2> grep-errors.txt" puts errors messages into a file.
     • "grep * 2>&1>out.txt" gets both.
  4. "|" strings together files. "find | grep avi" is a lazy way to find movie files.
  5. ls -l | grep "\.txt$" is a painful replacement for ls *.txt, but useful as above.
• evaluating stuff
  1. test
  2. conditional stagements and expressions, integers like fortran, strings like C, file operators are nice. if fi just like C. see example /condition/if.sh
• Loops
• Functions
• automating simple tasks