Bash: Get List of Commands Starting with a Given String

bash: get list of commands starting with a given string

You should be able to use the compgen command, like so:

compgen -A builtin [YOUR STRING HERE]

For example, "compgen -A builtin l" returns

let 
local 
logout

You can use other keywords in place of "builtin" to get other types of completion. Builtin gives you shell builtin commands. "File" gives you local filenames, etc.

Here's a list of actions (from the BASH man page for complete which uses compgen):

  alias      Alias names.  May also be specified as -a.
  arrayvar   Array variable names.
  binding    Readline key binding names.
  builtin    Names  of  shell builtin commands.  May also be specified as -b.
  command    Command names.  May also be specified as -c.
  directory  Directory names.  May also be specified as  -d.
  disabled   Names of disabled shell builtins.
  enabled    Names of enabled shell builtins.
  export     Names of exported shell variables.  May also be specified as -e.
  file       File names.  May also be specified as -f.
  function   Names of shell functions.
  group      Group names.  May also be specified as -g.
  helptopic  Help topics as accepted by the help builtin.
  hostname   Hostnames, as taken from the file specified by the HOSTFILE shell
                 variable.
  job        Job  names, if job control is active.  May also be specified as
                 -j.
  keyword    Shell reserved words.  May also be specified as -k.
  running    Names  of  running  jobs,  if  job  control  is active.
  service    Service names.  May also be specified as -s.
  setopt     Valid arguments for the -o option  to  the  set builtin.
  shopt      Shell  option  names  as  accepted by the shopt builtin.
  signal     Signal names.
  stopped    Names  of  stopped  jobs,  if  job  control  is active.
  user       User names.  May also be specified as -u.
  variable   Names  of  all  shell  variables.   May also be specified as -v.

In Bash, how can I check if a string begins with some value?

This snippet on the Advanced Bash Scripting Guide says:

# The == comparison operator behaves differently within a double-brackets
# test than within single brackets.

[[ $a == z* ]]   # True if $a starts with a "z" (wildcard matching).
[[ $a == "z*" ]] # True if $a is equal to z* (literal matching).

So you had it nearly correct; you needed double brackets, not single brackets.

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With regards to your second question, you can write it this way:

HOST=user1
if  [[ $HOST == user1 ]] || [[ $HOST == node* ]] ;
then
    echo yes1
fi

HOST=node001
if [[ $HOST == user1 ]] || [[ $HOST == node* ]] ;
then
    echo yes2
fi

Which will echo

yes1
yes2

Bash's if syntax is hard to get used to (IMO).

Find all files with a filename beginning with a specified string?

Use find with a wildcard:

find . -name 'mystring*'

Checking if output of a command contains a certain string in a shell script

Test the return value of grep:

./somecommand | grep 'string' &> /dev/null
if [ $? == 0 ]; then
   echo "matched"
fi

which is done idiomatically like so:

if ./somecommand | grep -q 'string'; then
   echo "matched"
fi

and also:

./somecommand | grep -q 'string' && echo 'matched'

Extract substring in Bash

Use cut:

echo 'someletters_12345_moreleters.ext' | cut -d'_' -f 2

More generic:

INPUT='someletters_12345_moreleters.ext'
SUBSTRING=$(echo $INPUT| cut -d'_' -f 2)
echo $SUBSTRING

Find all files with name containing string

Use find:

find . -maxdepth 1 -name "*string*" -print

It will find all files in the current directory (delete maxdepth 1 if you want it recursive) containing "string" and will print it on the screen.

If you want to avoid file containing ':', you can type:

find . -maxdepth 1 -name "*string*" ! -name "*:*" -print

If you want to use grep (but I think it's not necessary as far as you don't want to check file content) you can use:

ls | grep touch

But, I repeat, find is a better and cleaner solution for your task.

Linux command to list all available commands and aliases

You can use the bash(1) built-in compgen

• compgen -c will list all the commands you could run.
• compgen -a will list all the aliases you could run.
• compgen -b will list all the built-ins you could run.
• compgen -k will list all the keywords you could run.
• compgen -A function will list all the functions you could run.
• compgen -A function -abck will list all the above in one go.

Check the man page for other completions you can generate.

To directly answer your question:

compgen -ac | grep searchstr

should do what you want.

What linux shell command returns a part of a string?

If you are looking for a shell utility to do something like that, you can use the cut command.

To take your example, try:

echo "abcdefg" | cut -c3-5

which yields

cde

Where -cN-M tells the cut command to return columns N to M, inclusive.

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