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Questions tagged [shell-builtin]

A shell builtin is a command called from a shell, that is executed directly in the shell itself.

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1answer
25 views

How can I extract a function from bash/zsh with all its shell-related dependencies?

I write a lot of little useful functions, and sometimes I like to share them with friends or the world. The problem is that I use a lot of my helper functions and aliases in my functions, and I don't ...
1
vote
1answer
78 views

Password Encryption [duplicate]

I have a Migrate.ksh file, in that some passwords are available, I would like to encrypt this file in the Unix. The Passwords file being used in another script. Can you please let me know the process ...
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votes
2answers
74 views

rm -rf ./* deletes content of current directory only partially [duplicate]

rm -rf ./* deleted all content of current directory only partially. Input: MN> cd ~/mydir MN> rm -rf ./* MN> ll Output: -rw-r--r-- 1 MN MN 1025 Aug 1 15:50 .file1 -rw-r--r-- 1 MN MN ...
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1answer
39 views

How bash builtins works with pipeline

Bash builtins defines as: The shell executes the command directly, without invoking another program. And a pipeline like foo | bar works roughly like: bar waits inputs from foo, and foo exits ...
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1answer
111 views

Does a Linux command called (h) exist?

I read in an unofficial documentation about a Linux shell command called h: it was mentioned together with the help and man commands, without any explanation. So I tried it on my linux terminal but it ...
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0answers
24 views

send stdin to stderr for a time, then stop after timeout and discard: gnu textutils?

We have a very chatty application which says useful things during startup but then refuses to be quiet (useful logs are sent elsewhere). This interacts problematically with log rotation, snapshotting, ...
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1answer
54 views

Does a shell builtin command actually run the program from its path?

I was reading the marked answer from here : What is the difference between a builtin command and one that is not? Here he says : A built-in command is simply a command that the shell carries out ...
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2answers
48 views

Wait command works when pid doesn't exists

I'm facing an unexpected behaviour of the wait builtin. ~ ❯ sleep 1 & [1] 72009 ~ ❯ [1] + 72009 done sleep 1 ~ ❯ wait 72009 ~ ❯ echo $? 0 Although the PID doesn't exist anymore wait ...
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2answers
31 views

getting only the path out of `type -p prog` command

if I run nrolland@mactoasty ~ $ type -p skhd skhd is /usr/local/bin/skhd I can't compose it nicely with other command like nrolland@mactoasty ~ $ la `type -p skhd` ls: is: No such file or ...
9
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2answers
1k views

Understanding shell builtin commands

In in the bash manual, it's written that Builtin commands are contained >>> within <<< the shell itself Also, this answer states that A built-in command is simply a command that ...
0
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0answers
27 views

checked and silent acquisition of an fd with exec

How can I acquire an fd for reading with Bash so that I can branch on the exit code without any further side effects? This is success and failure without the branch: $ set -u # -ue actually $ exec {...
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4answers
160 views

Is there a bash builtin command which can show the environment variables of the current shell?

env and printenv are both external commands i.e. executable files, not bash builtins. The problem with them is that some environment variables (such as _, and I also wonder if there are more) which ...
1
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1answer
84 views

How to capture stderr of a bash keyword (e.g. time)?

I want to time reading bash history and put the result into a variable. Unfortunately, time (which is a shell keyword) prints the result to stderr, and apparently redirecting stderr from shell ...
3
votes
1answer
269 views

Need for the `builtin` builtin

What's the point of the builtin builtin when the command builtin has the exact same functionality when it comes to looking up builtins? When making sure that a particular builtin is chosen over a ...
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votes
1answer
44 views

`declare` un-causing problems with missing functions/commands?

summary: If in bash I attempt to assign the output of a missing function to a previously-declared (i.e., not {constant, read-only}) variable, I can detect the failure with "normal" tests. But if I ...
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0answers
46 views

Would a 'function_not_found_handle ()' loadable bash builtin be possible?

I wrote a function to handle unknown commands in bash via command_not_found_handle (). My intention is to source scripts on demand and access its functions inside the handler. But unfortunately the ...
3
votes
1answer
144 views

What do special characters stand for in echo {A..z}

I know we can print a sequence of letters of the Alphabet using echo command and experimented it a little by doing this. Lowercase letter Sequence $ echo {a..z} a b c d e f g h i j k l m n o p q r s ...
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1answer
117 views

dirs -v does not list the directory stack?

I have seen How do I use pushd and popd commands? , and I am aware that with pushd <dir> I would push <dir> to the directory stack, with popd I would pop the top directory from the ...
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1answer
54 views

What is the difference between shell builtins and shell keyboard shortcuts?

What is the difference between shell builtins (like cd or echo) and shell keyboard shortcuts (like ctrl+u or ctrl+l)? Both seems to me "builtins", what is the major difference by means of system ...
1
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0answers
27 views

What is the behavior of `command`? [duplicate]

According to this comment which is in defense of the author's answer, @einpoklum Yes, it is necessary. In fact, even this solution may break in one edge case. Thanks for bringing this to my ...
6
votes
2answers
582 views

How to bypass bash functions called `command`, `builtin` and `unset`?

I am aware that aliases can be bypassed by quoting the command itself. However, it seems that if builtin commands are "shadowed" by functions with the same names, there is no way to execute the ...
2
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1answer
27 views

Efficient stdin generation in shell script

Is there a more idiomatic way to express the following? xargs -r -l1 -I % bash -c 'cat <(echo %)' Where cat stands for intended program that does not accept relevant argument from command line, ...
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2answers
129 views

When a shell runs a builtin, and a signal is generated by keyboard, what will handle the signal?

Please correct me if I am wrong: When a bash shell runs an external executable program, the bash shell will create a child process to run the program in foreground. If there is any key-generated ...
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1answer
145 views

Shell Script for formatted output [closed]

06/26/2017 23:40:40 CAUAJM_I_10082 [aspsun14 connected for IOALPPRXXBD_ALPGLGENFAALL 55443.15215291.1] 06/26/2017 23:40:40 CAUAJM_I_40245 EVENT: CHANGE_STATUS STATUS: STARTING ...
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votes
2answers
321 views

How to distinguish between builtin and external util? (e.g. echo)

Some commands are provided as both builtins and external utilities. Take echo for example. On my machine (macOS) running Bash 3.2, $ type echo echo is a shell builtin Running man bash | less --...
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2answers
132 views

bash custom builtin

I am wanting to build a custom builtin in bash -- like time for example. Is this possible? If it's not, is it possible in another shell? For example, I want to do this: map find -name '*.js' | xargs ...
6
votes
1answer
1k views

What is the parameter “i” of the set command in the bash shell?

I looked up the shell builtin command set by typing help set, and the short syntax description shows: set [-abefhkmnptuvxBCHP] [-o option-name] [--] [arg ...] The help-documentation explains, ...
20
votes
2answers
3k views

What is the purpose of the bash `suspend` builtin command?

I typed help suspend and got this short explanation: suspend: suspend [-f] Suspend shell execution. Suspend the execution of this shell until it receives a SIGCONT signal. Unless forced, ...
1
vote
0answers
407 views

Why does 'typeset' not work for me but 'declare' does? [closed]

I switched the shell on my main account to zsh and when installing a script that logs history to a database, https://github.com/larkery/zsh-histdb, I saw that some typeset commands in them didn't work,...
1
vote
2answers
709 views

How to specifically run a shell builtin command

Consider a situation that I run these commands in my current shell or I put them inside .bashrc: alias source='echo hi' alias .='echo hi' alias unalias='echo hi' Or function source(){ echo hi; }, ...
44
votes
8answers
4k views

Why are POSIX mandatory utilities not built into the shell?

The purpose of this question is to answer a curiosity, not to solve a particular computing problem. The question is: Why are POSIX mandatory utilities not commonly built into shell implementations? ...
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1answer
24 views

Unexpected source (mis)behaviour

I have a file with my Raspberry Pi address named pi. It's in my home directory. pi=192.168.0.173 To connect to the Pi, I'd do this in my home directory: . pi && ssh pi@$pi It worked. Then ...
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votes
1answer
131 views

Any bash magic to reference the previously typed parameter? [duplicate]

This question is a variant on a previously asked How to repeat currently typed in parameter on bash console? Many a time, I find myself wanting to slightly rename a file name in the shell, e.g.: $ ...
10
votes
1answer
1k views

What is an “s” inside “$-”?

I'm normally well aware of the contents of $-. On a recent CentOS I get: [grochmal@orion ~]$ echo $- himBH hmBH are all options from set, and i means that my shell is interactive. Yet, on my Arch ...
2
votes
1answer
133 views

Why do shells implement their own “echo” commands internally? [duplicate]

(Note that this is entirely an academic question... I'm just curious about the answer, not trying to solve any particular problem.) From the ECHO(1) manual page (GNU echo): NOTE: your shell may ...
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votes
1answer
95 views

Redirection in self created linux shell [closed]

I am writing my own shell. I want to implement redirection( > and >>). For that I have used dup2() system call. But if a command I enter has redirection, another command follows the previous ...
2
votes
1answer
254 views

AIX - use ksh builtins to free memory when fork not possible

Context: an AIX lpar with very low memory (no forking possible, so only shell's builtins (cd, echo, kill) will work). I can have a (hmc) console to it, but I need a better way to start freing memory ...
62
votes
4answers
61k views

What's the difference between eval and exec?

eval and exec are both built in commands of bash(1) that execute commands. I also see exec has a few options but is that the only difference? What happens to their context?
9
votes
1answer
1k views

How can I get a help message for zsh builtin's?

If I want to get a brief usage message for a bash builtin, I can use help <builtin> at a command prompt, e.g. $ help export export: export [-fn] [name[=value] ...] or export -p Set export ...
1
vote
0answers
87 views

How to write decorator commands [duplicate]

I don't know the exact word, that's why I'll use "decorator", like in POO, but I'm talking about the kind of functions you can use before other functions to add any operations to it, like the command ...
0
votes
2answers
828 views

How does the shell decide which of same-name keyword, builtin, and external command to run? [duplicate]

When there are same-name builtin, keyword and/or external command, what is the order in which the Bash shell decides which to run? For example, keyword time and external command time, builtin ...
12
votes
4answers
1k views

Use case / practical example for Bash' builtin exec

Consider this from the documentation of Bash' builtin exec: exec replaces the shell without creating a new process Please provide a use case / practical example. I don’t understand how this makes ...
0
votes
1answer
68 views

How do I execute command to avoid interference from the shell [duplicate]

Sometimes a same command is provided by shell-builtin as well as other file/package. Example: $ type -a printf kill printf is a shell builtin printf is /usr/bin/printf kill is a shell builtin kill is ...
17
votes
5answers
2k views

Write output of `time` in a file, why are parentheses needed?

time writes to stderr, so one would assume that adding 2>&1 to the command line should route its output to stdout. But this does not work: test@debian:~$ cat file one two three four test@...
3
votes
2answers
130 views

Why builtin times doesn't work in pipeline?

I've the following sample script: #!/usr/bin/env bash sleep 5 printf "times cmd: " times printf "pipeline: " times | ( read user sys; echo $user; ) printf "head: " times | head -n1 printf "times cmd ...
12
votes
2answers
2k views

What does “is hashed” mean when using the type command? [duplicate]

I was reading this post and trying out all of the commands in the first answer... I don't really have anything else better to do right now. Anyways, I ran through them all in regards to rm. What ...
0
votes
1answer
228 views

Whatis command (shell builtin vs executable programs)

I know that whatis command is used to output a brief description about an executable program (Command). So both whatis cd whatis type Will print: nothing appropriate (Because from my ...
3
votes
2answers
1k views

The type command can't distinguish between an executable command and a shell script

So I was reading the book The Linux Command Line, and it says that commands are of four types: (1) executable programs (2) shell builtins (3) shell functions (shell scripts) (4) ...
6
votes
1answer
1k views

How to read the man page for a bash builtin? [duplicate]

So, I needed to figure out how "exec" works. However, doing man exec brings me to a 99% useless man page describing what bash builtins are. It of course also does this with many other man pages such ...
2
votes
3answers
69 views

How can I view the stack used by `pushd` and `popd`?

I would like to use the recently accessed directories list for logging purposes. Is the directory stack as used by pushd and popd stored somewhere, perhaps as a list of folders in a text file? If so, ...