advancedLinux.md

Advanced Linux

outline

1. Reminder on the structure of a command line: command name, parameters (short and long format) and arguments
2. Refresher on grep. Simple examples
3. Bash utilities like diff, cut, join
4. Variables and variable expansion with the $ sign. The effect of single- or double-quoting
5. Shell scripts
6. Tests and control structures. Things like if \[ $a -ne 0 ], loops (for and while)
7. String manipulation in Bash, with constructs like "${var:2:5}" or "${var%.tar} (see https://www.tldp.org/LDP/abs/html/string-manipulation.html)
8. Arithmetic calculations in Bash, with "expr" or constructs like "$(( var + 1 ))""
9. Simple file processing with sed.
10. awk.

sed

    `sed [-e] 'instruction' file`

The command line options are: -e Editing instruction follows. -f Filename of the script follows. -n Suppress automatic output of input lines. You can pass multiple sed commands by preceding each with -e or a semicolon (;)

` sed -e 's/old/new/' -e ’s/old1/new2/' file`

You can also pass commands to sed in a file using -f.

`sed -f sedcscript -e `

For further resources on sed, see: [Provide a good link]

awk

Named after the three developers.

awk 'instructions’ files

For example, in this example where sed works like cut,

awk '{ print $1 }' file, The instruction is to print the first field in the file. By default, the fields are delimited by space. Where another character delimits the fields, -F is used to specify the delimiter.

awk -F, '{ print $1 }' file (a comma in this example)

You can also print each field in its line by separating the print statements with a semicolon.

awk -F, '{ print $1; print $2; print $3 }' file