What constitutes internal commands from external commands?
Nothing tricky about it. External commands are external because they're external -- they're files, programs the shell runs. They exist whether you're running a shell or not. cd is a pure builtin, without any external equivalent -- by definition cd must be a builtin, it wouldn't work.
ls on the other hand is not a builtin -- it has binary executables and manual pages and stuff.
printf is both -- it is a builtin in most shells, for performance reasons since it's used often for tiny tasks. But the binary program also exists in case it's needed.
An extreme case is the busybox shell, which is intended to be a mini stand-alone UNIX system. It may have hundreds of builtins, including minimal versions of things like awk, sed, cp, mv, xargs, etc etc etc -- which traditionally have never been builtins.
So, the reason all these programs seem identical between shells is because your shell doesn't contain the universe, just talks to it.
what does this symbol ~ represent in unix for example....
If i create directories called personal and lab and lab5 and the command chmod 776~/lab5 is issued. What results would i expect to get. basically i know that chmod 776 would prevent others from executing the files in the directory but... (2 Replies)
Hi ,
i have few doubts about the braces and spaces which are quite often used:
for instance:
when i try the belo command it will not work
export variable= cat filename
rather when i try the cat command without any space it works fine
export variable=cat filename
and... (3 Replies)
Many scripts are executed in the following way.
. /scriptname
Even when the file does not have execute permission, it can be executed this way. How does this work? (6 Replies)
Hi,
I am a newbie in unix shell scripting and I am trying to understand the result of the following line :
ls -l $1*$4*ready
I understand the ls-l but the rest is just really confusing. Any help would be appreciated.
TIA (3 Replies)
this post is related to the arrangements of libraries in a solaris-8 distribution.
i want to build external packages on solaris-8
i need to know why libraries are scattered in a solaris distribution among different below mentioned directories,
please tell me whats the importance ??
/lib... (3 Replies)
Hello... I am getting ready to create a bunch of groups for several of our servers all of which are running Aix 5.3. We really want to keep people away from using the root login and as such the systems have been hardened using aixpert and if it is absolutely needed people must su -.
There are... (1 Reply)
What is the significance of the forward slash(/) while specifying a directory?
cp -av /dir/ /opt/
and
cp -av /dir /opt
Does effectively the same job it seems? (2 Replies)
Hi
I was trying to understand what ':-' means when used with variables
echo ${x:-10}
if
Thanks (4 Replies)
Discussion started by: zulfi123786
4 Replies
LEARN ABOUT REDHAT
whereis
WHEREIS(1) General Commands Manual WHEREIS(1)NAME
whereis - locate the binary, source, and manual page files for a command
SYNOPSIS
whereis [ -bmsu ] [ -BMS directory... -f ] filename ...
DESCRIPTION
whereis locates source/binary and manuals sections for specified files. The supplied names are first stripped of leading pathname compo-
nents and any (single) trailing extension of the form .ext, for example, .c. Prefixes of s. resulting from use of source code control are
also dealt with. whereis then attempts to locate the desired program in a list of standard Linux places.
OPTIONS -b Search only for binaries.
-m Search only for manual sections.
-s Search only for sources.
-u Search for unusual entries. A file is said to be unusual if it does not have one entry of each requested type. Thus
`whereis -m-u *' asks for those files in the current directory which have no documentation.
-B Change or otherwise limit the places where whereis searches for binaries.
-M Change or otherwise limit the places where whereis searches for manual sections.
-S Change or otherwise limit the places where whereis searches for sources.
-f Terminate the last directory list and signals the start of file names, and must be used when any of the -B, -M, or -S options are
used.
EXAMPLE
Find all files in /usr/bin which are not documented in /usr/man/man1 with source in /usr/src:
example% cd /usr/bin
example% whereis -u -M /usr/man/man1 -S /usr/src -f *
FILES
/{bin,sbin,etc}
/usr/{lib,bin,old,new,local,games,include,etc,src,man,sbin,
X386,TeX,g++-include}
/usr/local/{X386,TeX,X11,include,lib,man,etc,bin,games,emacs}
SEE ALSO chdir(2V)BUGS
Since whereis uses chdir(2V) to run faster, pathnames given with the -M, -S, or -B must be full; that is, they must begin with a `/'.
whereis has a hard-coded path, so may not always find what you're looking for.
8 May 1994 WHEREIS(1)