[bash] do not use 'ls' to loop through dir files, use glob

ParsingLs
bash shopt man page

touch 'a space' $'a\nnewline'
echo "don't taze me, bro" > a
ls | cat

result:
a
a
newline
a space

---

using:
# shopt -s nullglob
to prevent generating literal '*' if directory has no files.

# Good! (Bash-only)
shopt -s nullglob
for f in *; do
    ...
done

[bash] [ test

Why do I need to quote variable for if

What is the difference between [[ $a == z* ]] and [ $a == z* ]?

Bash ADV

• 0xff or o12 does not evaluated in [ command
• always quote variables in [ command
• never use the -a or -o operator (use several [ commands and the && and || shell operators)
• The whole [[ ... ]] construct makes up a command.

[bash] "<<<"

Redirector “<<<”


3.6.7 Here Strings

A variant of here documents, the format is:

<<< word

The word is expanded and supplied to the command on its standard input.

[bash] log messages

How to properly use log_daemon_msg, log_end_msg, log_progress_msg to write a proper daemon script?
LSB Init Script Functions (5.0.0)

[bash] status command

sudo status bconfigagent

[bash] ls show timestamp

ls -lh --time-style +%s /etc/nimbula/node.conf /etc/nimbula/site.conf-age

[bash] concatenate string variables in Bash

how-can-i-concatenate-string-variables-in-bash

[BASH] print out a variable in makefile through make argument

[SO] How to print out a variable in makefile

print-%  : ; @echo $* = $($*)

make print-VARIABLE

[bash] extended pattern matching bash

shopt -s extglob

man shopt



?(pattern-list) Matches zero or one occurrence of the given patterns

*(pattern-list) Matches zero or more occurrences of the given patterns

+(pattern-list) Matches one or more occurrences of the given patterns

@(pattern-list) Matches exactly one of the given patterns

!(pattern-list) Matches anything except one of the given patterns

[bash] tips

Not recommended is using sh < scriptname, since this effectively disables reading from
stdin within the script.

;
Command separator [semicolon]. Permits putting two or more commands on the same line.

echo hello; echo there
if [ -x "$filename" ]; then # Note the space after the semicolon.

;;
Terminator in a case option [double semicolon].

case "$variable" in
abc) echo "\$variable = abc" ;;
xyz) echo "\$variable = xyz" ;;
esac

:
null command [colon]. This is the shell equivalent of a "NOP" (no op, a do-nothing operation). It
may be considered a synonym for the shell builtin true. The ":" command is itself a Bash builtin, and
its exit status is true (0).

()
command group.

(a=hello; echo $a)

A listing of commands within parentheses starts a subshell.

#!/bin/bash
# Reading lines in /etc/fstab.
File=/etc/fstab
{
read line1
read line2
} < $File
echo "First line in $File is:"
echo "$line1"
echo
echo "Second line in $File is:"
echo "$line2"
exit 0

{
echo # End code block.
} > "$1.test" # Redirects output of everything in block to file.

{} placeholder for text. Used after xargs -i (replace strings option). The {} double curly brackets are a placeholder for output text.

ls . | xargs -i -t cp ./{} $1
# ^^ ^^

If COMMAND contains {}, then find substitutes the full path name of the selected file for "{}".

find ~/ -name 'core*' -exec rm {} \;
# Removes all core dump files from user's home directory.

# "2>/dev/null" hides error message.

2>/dev/null;

The (( )) construct expands and evaluates an arithmetic expression. If the expression evaluates as zero, it returns an exit status of 1, or "false". A non-zero expression returns an exit status of 0, or "true". This is in marked contrast to using the test and [ ] constructs The == comparison operator behaves differently within a double-brackets test than within single brackets.

[[ $a == z* ]] # True if $a starts with an "z" (pattern matching).
[[ $a == "z*" ]] # True if $a is equal to z* (literal matching).
[ $a == z* ] # File globbing and word splitting take place.
[ "$a" == "z*" ] # True if $a is equal to z* (literal matching).