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Other useful Commands and Programs

ypchsh : To switch your shell globally. Default is tcsh.
chmod : To change the attribute of a file or a directory.
Usage: chmod [ugoa][+-][rwx] file
For instance if you don't want others to read your file,
```
 
chmod o-r your_file
```
That is, ``change the mode of your_file so that others can't (-) read it''.
u is the user, that's you. a is all and g is group. + adds the attributes, - subtracts them, w is write privilege, x is execute privilege.
To check filesystem disk space usage
df
To check your own disk space usage
du
To add a directory to the command path : Edit the .tcshrc file in your home dir. For instance, add
```
 
 set path = (. $path)
```
if you want to put the current directory before the default path or
```
 
 set path = ($path .)
```
to put it after the default path.
To convert one graphics format to another
```
 
 convert picture.eps picture.jpg
```
This converts picture.eps to picture.jpg. The known formats are .ps, .eps, .pdf, .png, .pnm, .gif, .jpg, .tiff, etc. If convert is not installed on your machine, do
```
 
 which pngtopnm
```
and note in which directory pngtopnm is in. Go there and ls. You should see 200+ converters for almost all combinations.
To convert a ps file to an epsi file
```
 
 ps2epsi picture.ps
```
This produces picture.epsi.
To convert a ps file to an ascii file
```
 
 ps2ascii paper.ps output.txt
```
This extracts text from paper.ps.
To view a graphics file
```
 
 display picture.jpg
```
If display is not installed, then use xv.
nice : To be nice to other people using the same machine
```
 nice prog_name
```
so that your program does not hog all the resources.
> and < : Redirect. If a program takes standard input (STDIN) from the keyboard, you can create a file with all the data and do
prog < input_dat
and the program will take the lines in input_dat as if it is given at the command prompt followed by return.
If the program prints out to the standard output (STDOUT) or on your screen, you can redirect it to a file using > output_data. Namely
```
 prog < input_data > output_data
```
Note that redirect destroys output_data. If you want to append to the file use >> output_data.
Pipe | : Pipe is used when you want to string programs that take a file as an input but writes on to STDOUT. Take a look at this example. Suppose you have a jpeg file you want to convert to a png file. And suppose your convert does not function somehow. Now there is this command
```
 jpegtopnm picture.jpg
```
which writes out a pnm file to STDOUT, or on your screen. Don't try this. It'll mess up your screen. You can always redirect it
```
 jpegtopnm picture.jpg > picture.pnm
```
then use
```
 pnmtopng picture.pnm > picture.png
```
again redirecting it to a file. This process, however, can be short-circuited using pipe:
```
 jpegtopnm picture.jpg | pnmtopng > picture.png
```
This is also very useful when a program produces a massive amount of output that just flies by. In that case try
```
 prog_name | less
```
You can then treat the output of this program as if it is a file and use less to navigate around.
grep : To globally search regular expression and print the line. Or in English, grabs line that contains a word or phrase from a file or files and writes to STDOUT.
```
 grep word file.txt

 or

 grep "A word with you, sir." file*.txt
```

Next: About this document ... Up: unix_guide Previous: Getting More Information

Sangyong Jeon 2007-09-18