1. CIRC Summer School 2017 Baowei Liu 7.25.2017
Bash Scripting
CIRC Summer School 2017
Baowei Liu

2. Stdin, stdout and stderr
File descriptor(FD): a handle to access a file
Stdin: standard input stream (e.g. keyboard) –FD:0
Stdout: standard output stream (e.g. monitor) –FD:1
Stderr: standard error output stream (usually also on monitor) ) –FD:2

3. I/O Redirection: Redirecting to a file
Redirect between files including the three file descriptors, stdin, stdout and stder
Redirecting output: date > file
Appending redirecting output: date >> file
Redirecting input: Command < input

4. I/O Redirection: Pipes
Pipes connect the standard output of one command to the standard input of another with the pipe symbol |.
command1 | command2

5. Positional Parameters
Arguments given to bash script when it is invoked
$1, $2 … $N. ${N} if N>9
$0 is the base-name of the script
$# is the total arguments given
Example: shareFiles.sh positionalParameters.sh

6. grep
grep: search for matches to a pattern in a file and print the matched line to stdout
grep Pattern file
Pattern could be simple strings or regular expressions

7. Regular Expression Regular Expression: globbing pattern used for text
. : Equivalent to ? in filename expansion
* : zero or more times, aa* will match a,aa,…but not ab
.*: any string. Equivalent to * in filename expansion
^: starting with, ^ab
$: ending with, ab$

8. Regular Expression
[]: “-”
\< \>: exact word

9. sed and Regular Expressions
Stream editor for parses and transform text
sed ‘s/abc/xyz/’ File: first occurrences
sed ‘5,10s/abc/xyz/’ File: range, specified lines
Sed ‘0~2 s/abc/xyz/’ File: Every other line starting 0 or even lines

10. sed and Regular Expressions
Word Characters: Alphanumeric characters plus “_” [A-Za-z0-9_]
Replace all occurrences in a line

11. More Examples
Wrappers

12. Project
Write a Bash script to black out sensitive information buried in all but the .data files under files/ (i.e. ONLY the html,xml,txt files)
Key tech: editor, chmod, command substitution, for loop, echo, case/if, string compare, substring remove, sed, regular expression, i/o redirection