Week 2

globbing, grep, and intro to bash scripting

Glob Constructs, Meta-Chars, & Special-Chars

globbing : used for matching or expanding specific types of patterns

• mostly used to match filenames or searching for content in a file.

• uses wildcard characters (?, * , [], ^, !, $, {}, |,) to create the pattern:

• ? - matches single character (1-1)

  • ex. match any 4-char .txt file : ls ????.txt

  • ex. match any file w/ 4-char name & 2-char ext : ls ????.??

  • ex. ls week?.txt can match week1.txt, ... weekN.txt

• * - matches N-characters (1-N)

  • ex. match any file w/ .tsx ext : ls *.tsx

  • ex. match any file that starts w/ "a" : ls a*.*

• [] - matches any character from range

  • range of:

    • all uppercase alphabets : [:upper:] or [A-Z]

    • all lowercase alphabets : [:lower:] or [a-z]

    • all numeric alphabets : [:digit:] or [0-9]

    • all alphabets : [:alpha:] or [a-zA-z]

    • all the above: [:alnum:] or [a-zA-Z0-9]

  • ex. match any file that starts w p/q/r/s : ls [p-s]*

  • ex. match any file that starts w 1/2/3/4/5 : ls [1-5]*

  • ex. ls prog[1-58].c => possible: prog1.c, prog34.c

  • ex. ls *[-]* => possible: prisma-api.md, redux-tk.md

• ! - exclude

  • [!ABC] : matches any single char except A, B or C

  • [!a-z0-4] : matches any single char except a,...z, 0, ...4

• Character Classes

  • [:alnum:] [:alpha:] [:blank:] [:cntrl:] [:digit:] [:graph:] [:lower:] [:print:] [:punct:] [:space:] [:upper:] [:xdigit:]

  • ex. match any file that starts w/ a A-Z : ls [[:upper:]]*

  • ex. combine multiple classes: ls lab[[:digit:][:lower:]].* (0-9 & a-z)

• Specials Characters:

  • ~ : your home directory name (/home/dwoit in my case)

  • ~usr : the home dir of user with userid "usr"

  • ~- : your previous working dir (note in bash cd - same as cd ~-)

  • ~+ : your current working dir

  • \ : ignore glob construct following (like "" or '')

    • ex. echo /[abc]* outputs: [abc]*

  • \ : at end of line, means command continues on next line

• Patterns & RegEx

  • *(exp) : 0 >= occurrences of exp

  • +(exp) : 1 >= occurrences of exp

  • ?(exp) : 0 / 1 occurrences of exp

  • !(exp) : anything that does not match exp

  • @(exp1|exp2|...) : anything that matches exp1 or exp2 or ...

Bash Scripting

Running .sh Scripts

$ sh myscript

Alternatively, in your myscript.sh file, do the following

#!/bin/sh
chmod u+x myscript    # sets 'executable' flag on the file

and run it with...

$ ./myscript

Arguments

Arguments can be passed into a script as you would w/ any bash command.

$ ./myscript foo bar baz    # params spaced after filename

• $# : number of args (3)

• $n: param name (n is the number)

  • eg. $1 = "foo"

• $*: One string with all parameter names

  • "foo bar baz"

• $@: Comma seperated strings for each parameter name

  • "foo", "bar", "baz"

• shift: Shifts Positional Parameters by 1

Grep

Global Regular Expression Print

syntax : grep string filename(s)

• string : string to search for

• filename(s) : files to search string in

  • w/o file, grep will read from stdin until EOF

Displays the lines of the file containing the string

# search for string in 1 file
$ grep "editor" vimTutorial.txt

    In this lab you will learn to use the vim editor by actually
    This exits the editor, DISCARDING any changes you have made.
    # and so on....

# search for string in 2 files
$ grep "scanf" waterTemp.c switch.c

# filename:        line contents
waterTemp.c:     scanf("%lf", &tmp);
switch.c:        scanf("%c", &letter);

Options

• -i : ignore case

• -v : print liens not matching search string

• -x : search string must match entire line

Metacharacters

• . : like ? in glob (subs in any char)

• * : 0 or more reps of previous char (not like * in glob)

• ^ : patten must be at the start of the line (ie. "^Raiders")

• $ : pattern must be at the end of a line (ie. "Chargers$")

• \{m\} : exactly m reps of previous char (ie. "x\{3\}")

• \{m,\} : atleast m reps of previous char

• \{m,n\} : between m to n reps of previous char (inclusive)

• \< : line has word that starts w/ character (ie. "\<x")

• \> : line has word that ends w/ character (ie. "x\>")

# examples

grep '^Assignment' fname # lines starting with Assignment
grep -v '^Assignment' fname # lines not starting with Assignment
grep 'Assignment$' fname # lines ending with Assignment
grep 'd.g' fname # lines containing dag, dbg, dcg, d0g, d1g, etc
grep 'su*m' fname # lines containing sm, sum, suum, suuum, etc
grep 'suu*m' fname # lines containing sum, suum, suuum, etc
grep '\<so\>' fname # the word so (vs. social, absolute)
grep '[A-Za-z][A-Za-z]*' fname # lines containing ANY non-empty alpha string
grep '^[A-Za-z][A-Za-z]*$' fname # lines containing ONLY alpha characters
grep 'xyz\.w\{2,3\}X' # lines containing xyz.wwX or xyz.wwwX
grep 'A(bc)\{2,3\}D' # lines containing AbcbcD or AbcbcbcD
grep -x "abc" # lines that contain exactly and only abc