let built-in doesn't work as expected
in [Shell]
|
Prev: Can I pass the output of some command to two or more commandswithout using a temporay file?
Next: let built-in doesn't work as expected
From: Jeenu on 18 Apr 2008 01:35 Hi, I have a file (myfile) containing the following lines: a = 1 b = 2 c = 3 now if I do: cat myfile | while read LINE; do let "$LINE" done AFAIK, I should get the environment variables a, b and c, but it these variables don't get assigned at all. Could somebody please tell me why this is happening? Or isn't this the right way to use the 'let' built- in? Thanks Jeenu
From: Bill Marcum on 18 Apr 2008 02:03 On 2008-04-18, Jeenu <jeenuv(a)gmail.com> wrote: > > > Hi, > > I have a file (myfile) containing the following lines: > > a = 1 > b = 2 > c = 3 > > now if I do: > > cat myfile | while read LINE; do > let "$LINE" > done > > AFAIK, I should get the environment variables a, b and c set to the > values, but these variables don't get assigned at all. Could somebody > please tell me why this is happening? Or isn't this the right way to > use the 'let' built-in? > > Thanks > Jeenu You should not have spaces before or after the = sign. Also, which shell are you using? In most shells, when you use a pipe, every process in the pipeline is executed in a subshell. In ksh or zsh, the last process in the pipeline is not a subshell.
From: Janis on 18 Apr 2008 03:45 On 18 Apr., 07:35, Jeenu <jee...(a)gmail.com> wrote: > Hi, > > I have a file (myfile) containing the following lines: > > a = 1 > b = 2 > c = 3 > > now if I do: > > cat myfile | while read LINE; do > let "$LINE" > done > > AFAIK, I should get the environment variables a, b and c, but it these > variables don't get assigned at all. Is there a difference in your (which one?) shell when doing... while read LINE; do let "$LINE" done <myfile Janis > Could somebody please tell me why > this is happening? Or isn't this the right way to use the 'let' built- > in? > > Thanks > Jeenu
From: Skye Shaw! on 18 Apr 2008 04:07 On Apr 17, 10:35 pm, Jeenu <jee...(a)gmail.com> wrote: > Hi, > > I have a file (myfile) containing the following lines: > > a = 1 > b = 2 > c = 3 > > now if I do: > > cat myfile | while read LINE; do > let "$LINE" > done > > AFAIK, I should get the environment variables a, b and c, but it these > variables don't get assigned at all. Could somebody please tell me why > this is happening? Or isn't this the right way to use the 'let' built- > in? > > Thanks > Jeenu What are you trying to do? let is for arithmetic evaluation, Do you mean set? [sshaw(a)localhost ~]$ cat bs.sh y=1 x=$y+23 echo $x let x=$y+23 echo $x a=1 echo $a a = 1 #oops, extra spaces [sshaw(a)localhost ~]$ bash bs.sh 1+23 24 1 bs.sh: line 8: a: command not found For assignments to bee seen by other processes, you must export them via export or set -a -Skye
From: pk on 18 Apr 2008 04:10
On Friday 18 April 2008 07:47, Jeenu wrote: > Hi, > > I have a file (myfile) containing the following lines: > > a = 1 > b = 2 > c = 3 > > now if I do: > > cat myfile | while read LINE; do > let "$LINE" > done > > AFAIK, I should get the environment variables a, b and c set to the > values, but these variables don't get assigned at all. Could somebody > please tell me why this is happening? Or isn't this the right way to > use the 'let' built-in? Try this: $ eval $(tr -d ' ' < myfile) $ echo "$a -- $b -- $c" 1 -- 2 -- 3 Remember to use eval only if you're 100% sure that what you're going to execute is safe. -- All the commands are tested with bash and GNU tools, so they may use nonstandard features. I try to mention when something is nonstandard (if I'm aware of that), but I may miss something. Corrections are welcome. |