I have a pipe of commands and I use "sudo sh -c" for getting sudo permission throughout the whole pipe commands.
The problem that I am facing is that commands like awk have different behaviour when "sudo sh -c" is used.
In particular,
sudo wc -c Mybib.bin |sudo awk '{print $1;}'
gives 1509644
while
sudo sh -c "wc -c Mybib.bin |awk '{print $1;}'"
gives 1509644 Mybib.bin
So, in the second case looks like the awk command is not invoked at all.
Thanks for any help.
It is, but the double quotes are allowing the $1 to be replaced before invocation, resulting in {print ;}.
sudo sh -c "wc -c Mybib.bin |awk '"'{print $1;}'"'"
Also...
sudo sh -c "wc -c < Mybib.bin"
I also found that you can escape the elements in sh -c as well.
For example:
sudo sh -c "wc -c Mybib.bin |awk '{print \$1;}'"
At least..that's working for me right now with a problem I ran into that was similar to yours.
Related
I am trying to execute the following command but the output is not coming as required.
var=$(echo "<password>"|sudo -S su -l <user> -c "<command>")
Please help if anyone can?
Expected Result:
var=$(echo ""|sudo -S su -l -c "pwd")
echo $var /home/bhushan
$:
Actual Result:
echo $var
$:
You can use backticks
var=`sudo -S su -l -c ""`
or the $(command) syntax
var=$(sudo -S su -l -c "")
(keep in mind though that sudo -S su -l -c "" doesn't output anything so $var will be empty)
You can workaround it by storing the output of the command into a file, then change its permission so that all users will see it and in a following command load it from the file:
sudo -S "<command> > /tmp/sudocmd.out && chmod 644 /tmp/sudocmd.out"
var=$(cat /tmp/sudocmd.out)
In order to identify if my installation has errors that I should notice, I am using grep command on the file and write the file using tee because I need to elevate permissions.
sudo grep -inw ${LOGFOLDER}/$1.log -e "failed" | sudo tee -a ${LOGFOLDER}/$1.errors.log
sudo grep -inw ${LOGFOLDER}/$1.log -e "error" | sudo tee -a ${LOGFOLDER}/$1.errors.log
The thing is that the file is created even if the grep didn't find anything.
Is there any way I can create the file only if the grep found a match ?
Thanks
You may replace tee with awk, it won't create file if there is nothing to write to it:
... | sudo awk "{print; print \$0 >> \"errors.log\";}"
But such feature of awk is rarely used. I'd rather remove empty error file if nothing is found:
test -s error.log || rm -f error.log
And, by the way, you may grep for multiple words simultaneously:
grep -E 'failed|error' ...
Why is echo showing the command and not the output of the command once I start using it in a FOR I loop? For example this command works
root#linux1 tmp]# iscsiadm -m node |awk '{print $1}'
192.168.100.88:326
But not in a FOR I loop
[root#linux1 tmp]# for i in 'iscsiadm -m node | awk '{print $1}'';do echo $i;done
iscsiadm -m node | awk {print
}
I want the command to print the first field so then I can add other functionality to the For I loop. Thanks
EDIT -- Not sure why I got voted down on this question. Please advise.
You're not executing the iscsiadm and awk commands, because you quoted it; that makes it a literal string. To substitute the output of a command back into the command line, use $(...)
for i in $(iscsiadm -m node |awk '{print $1}'); do
echo $i
done
I'm trying to write a simple bash script that executes a command with one string variable. Upon execution bash adds single quotes to the string variable making the command useless. How do I execute the command without the quotes from the bash script?
#!/bin/bash
key=$(echo $1 | tr '[:lower:]' '[:upper:]')
sudo tee /proc/acpi/bbswitch \<\<\<$key
the output I get is
~/scripts$ bash -x nvidia on
++ echo on
++ tr '[:lower:]' '[:upper:]'
+ key=ON
+ sudo tee /proc/acpi/bbswitch '<<<ON'
the two commands I want to run without the quotes are either
sudo tee /proc/acpi/bbswitch <<<ON
or
sudo tee /proc/acpi/bbswitch <<<OFF
The problem isn't the quotes, it's that sudo doesn't execute the command via the shell. So metacharacters like <<< don't have any special meaning when they're given as sudo arguments. You need to invoke the shell explicitly:
sudo bash -c "tee /proc/acpi/bbswitch <<<$key"
But there doesn't really seem to be a need to use a here-string for this. Just use:
echo "$key" | sudo tee /proc/acpi/bbswitch
There's no need to quote the <<< operator. sudo doesn't read from its standard input by default; it passes it through to the command it runs.
sudo tee /proc/acpi/bbswitch <<< $key
I have to concatenate a set of files. Directory structure is like this:
root/features/xxx/multiple_files... -> root/xxx/single_file
what i have written (and it works fine):
for dirname in $(ls -d root/features/*|awk -F/ '{print $NF}');do;mkdir root/${dirname};cat root/features/${dirname}/* > root/${dirname}/final.txt;done
But when i run the same thing via sh shell
/bin/sh -c "for dirname in $(ls -d root/features/*|awk -F/ '{print $NF}');do;mkdir root/${dirname};cat root/features/${dirname}/* > root/${dirname}/final.txt;done"
it gives me errors:
/bin/sh: -c: line 1: syntax error near unexpected token `201201000'
/bin/sh: -c: line 1: `201201000'
My process always appends /bin/sh -c before running any commands. Any suggestions what might be going wrong here? Any alternate ways? I have spent a really long time on this ,without making much headway!
EDIT:
`ls -d root/features/*|awk -F/ '{print $NF}' returns
201201
201201000
201201001
201201002
201201003
201201004
201201005
201201006
201201007
201202000
201205000
201206000
201207000
201207001
201207002
Always use sh -c 'cmd1 | cmd2' with single quotes.
Always use sh -eu -xv -c 'cmd1 | cmd2' to debug.
Always use bash -c 'cmd1 | cmd2' if your code is Bash-specific (cf. process substitution, ...).
Remove ; after do in for ... ; do; mkdir ....
Escape possible single quotes within single quotes like so: ' --> '\''.
(And sometimes just formatting your code clarifies a lot.)
Applied to your command this should look somewhat like this ...
# test version
/bin/sh -c '
for dirname in $(ls -d /* | awk -F/ '\''{print $NF}'\''); do
printf "%s\n" "mkdir root/${dirname}";
printf "%s\n" "cat root/features/${dirname}/* > root/${dirname}/final.txt";
echo
done
' | nl
# test version using 'printf' instead of 'ls'
sh -c '
printf "%s\000" /*/ | while IFS="" read -r -d "" file; do
dirname="$(basename "$file")"
printf "%s\n" "mkdir root/${dirname}";
printf "%s\n" "cat root/features/${dirname}/* > root/${dirname}/final.txt";
echo
done
' | nl
I got this to run in the little test environment I set up on my box. Turns out it didn't like the double quotes. The issue I ran into was the quotes around the awk statement...if you wrap it in double quotes it prints the whole thing.....I used cut to get the desired result, but my guess is you'll have to change the -f arg to 3 instead of 2..I think.
/bin/sh -c 'for dirname in $(ls -d sh_test/* | awk -F/ '\''{print $NF}'\''); do mkdir sh_test_root/${dirname}; cat sh_test/${dirname}/* > sh_test_root/${dirname}/final.txt;done'
edit: Tested edit proposed by nadu and it works fine. The above reflects that change.