More UNIX

.cshrc / .bashrc

Defines settings for all Shell sessions, including all invocations of a shell script.
Beware recursion: Do not call a shell script in here.

.login / .profile

Runs once, when you log in.
Like AUTOEXEC.BAT on DOS.
Can call a shell script in here.

DCU Linux - How to change the prompt

edit .bashrc

Example:

PS1='\W> '

See:

bash prompt format

Pipes and redirection

Very powerful features.

Pipes - Send output of one program to input of other.

e.g. Search for all lines in the file that contain "DCU" in any case, except those containing "Computing" in any case, and sort the remaining lines:

cat file | grep -i dcu | grep -iv computing | sort

Backquotes - Capture the output of a program as a string:

echo Current directory is `pwd` and date is `date`

Redirection - Read input from a file, send output to a file.

prog < inputfile > outputfile

cat file | grep -i student > studentlist
cat file | grep -i staff   > stafflist

Append:

cat morestuff >> studentlist

Unix pipeline

Filename completion

Start typing filename, hit special key to complete it.

DCU Solaris - Esc
DCU Linux - Tab
- If typing command - will search whole PATH for matches
- If just listing a file - will only search current dir

History


h         history of recent commands (numbered)
!n        replay command number n
!string   replay last command beginning with string
!!        last command

examples
!6 | sort
!ls | grep -v html

UNIX Philosophy

Unix philosophy
Provide lots of tools. String together tools with Shell logic, pipes, redirection.
all lower case - fast typing, don't have to hit Shift key
short command names - fast typing
Silence, "low-noise environment".
rm all my files, and it just does it. Doesn't even display a message saying they have been removed.
Note that backquotes would be useless if all programs displayed lots of informational messages as they executed.
Often an explicit prog -v "verbose" option if you want to see informational messages as it executes. But this is never the default.

Mac / Windows Philosophy

If not in the pre-installed menus, then hard luck. You can't do it.
High-noise.
rm all my files - dialog box comes up. Are you sure? OK.

Note that user interface people say these dialogs are often ignored.
From Donald Norman, The Psychology of Everyday Things, 1988, Ch.5:

Human - Delete all my most important files. System - Are you sure? Human - Yes Yes. System - Are you really sure? Human - Yes Yes. System - All your most important files deleted. Human - Oh damnit.

Compare with UNIX:

Human - Delete all my most important files. System - (Silence.) Human - Oh damnit.

Command-line on Mac / Windows

Windows always had DOS command-line, and still does.
But it has been little updated in 20 years.
Not as powerful as UNIX command-line.
Mac for years had no command-line at all.
But now has UNIX command-line.
Typical modern Mac has powerful UNIX command-line with bash, csh.