I have what I am assuming to be a very simple problem. I have used the following command in scripts many times before without issues.
display=/some/file/with/data
sed -i "s/$(more ${display} | grep 110 | gawk '{ print $3 }')/"replacestring"/g" ${display}
Never had an issue with this command.
I created a script that simplified everything that was needed and have the following code:
displayText=$(more ${display} | grep 110 | gawk '{ print $3 }')
I keep receiving
line 2: syntax error: unexpected end of file.
I am very familiar with Linux so the problem has been quite irritating as the answer has escaped me. Please assist.
Not sure why you are using more.
You also have backquotes around the awk script where you should have single quotes.
displayText=$(cat ${display} | grep 110 | gawk '{ print $3 }')
You will be told that this is a useless-use-of-cat (the cat command isn't needed since grep can read a file). You can just do:
displayText=$(grep 110 ${display} | gawk '{ print $3 }')
As awk can also search, this can be simplified further into:
displayText=$(gawk '/110/ {print $3}' ${display})
Related
my command run fine:
free -h -w | awk '{print $7}'
but how I can run using watch:
watch -n.6 "free -h -w | awk '{print $7}'"; ???
(that retun error)
PD:
yes, I want only column available from free
You can see the problem if you try what you posted. Look at the watch output. I see something like this:
Every 2.0s: free -h -w | awk '{print }'
The $7 is being resolved to nothing before watch gets to it.
You need to escape the $7 somehow.
This seems to work for me:
watch "free -h -w | awk '{print \$7}'"
How about putting \ in front of $7? i.e.,
watch -n.6 "free -h -w | awk '{print \$7}'";
The code without \ does not work because $7 is expanded in the double quotes. The shell tries to replace $7 (a positional parameter) with its content, which is likely to be blank. So in effect, you are running something like ... awk '{print }'.
What error are you receiving?
You are almost there, you just need a backslash in front of the $7
watch -n.6 "free -h -w | awk '{print \$7}'";
Escape the $ by using a backslash: \
watch -n.6 "free -h -w | awk '{print \$7}'";
That said, you still won't get the desired output, since not all the values are on the 7'th column. Consider a /proc/meminfo alternative;
awk '/MemFree/ { printf "%.3f \n", $2/1024/1024 }' /proc/meminfo
Using watch:
watch "awk '/MemFree/ { printf \"%.3f \n\", \$2/1024/1024 }' /proc/meminfo"
I have CSV columns that I'm working with:
info,example-string,super-example-string,otherinfo
I would like to get:
example-string super example string
Right now, I'm running the following command:
awk -F ',' '{print $3}' | sed "s/-//g"
But, then I have to paste the lines together to combine $2 and $3.
Is there anyway to do something like this?
awk -F ',' '{print $2" "$3}' | sed "s/-//g"
Except, where the sed command is only performed on $3 and $2 stays in place? I'm just concerned later on if the lines don't match up, the data could be misaligned.
Please note: I need to keep the pipe for the SED command. I just used a simple example but I end up running a lot of commands after that as well.
Try:
$ awk -F, '{gsub(/-/," ",$3); print $2,$3}' file
example-string super example string
How it works
-F,
This tells awk to use a comma as the field separator.
gsub(/-/," ",$3)
This replaces all - in field 3 with spaces.
print $2,$3
This prints fields 2 and 3.
Examples using pipelines
$ echo 'info,example-string,super-example-string,otherinfo' | awk -F, '{gsub(/-/," ",$3); print $2,$3}'
example-string super example string
In a pipeline with sed:
$ echo 'info,example-string,super-example-string,otherinfo' | awk -F, '{gsub(/-/," ",$3); print $2,$3}' | sed 's/string/String/g'
example-String super example String
Though best solution will be either use a single sed or use single awk. Since you have requested to use awk and sed solution so providing this. Also considering your actual data will be same as shown sample Input_file.
awk -F, '{print $2,$3}' Input_file | sed 's/\([^ ]*\)\([^-]*\)-\([^-]*\)-\([^-]*\)/\1 \2 \3 \4/'
Output will be as follows.
example-string super example string
This question already has answers here:
Piping tail output though grep twice
(2 answers)
Closed 4 years ago.
Here is my sample log file.http://pastebin.com/DwWeFhJk.
When I am doing
tail -f log | awk '{if (NF>3) {print $1}; }'
the result I am getting is correct
64.242.88.10
64.242.88.10
64.242.88.10
64.242.88.10
64.242.88.10
64.242.88.10
64.242.88.10
64.242.88.10
64.242.88.10
64.242.88.10
But when I am doing:
tail -f log |
awk '{if (NF>3) {print $1}; }' |
awk '{print $1}'
I am not getting any output. Even no output in case of
tail -f log | awk '{if (NF>3) {print $1}; }' | grep "64"
I am not getting the reason why the output of the first awk is not getting passed as the input of the second awk/grep after the pipe.
When the output of the first awk is going to the terminal, the output is line-buffered, so each line is printed as it is produced. When the output is going to the second awk or the grep, it is fully buffered. The output won't be sent until the buffer is full. When enough extra records are appended to the log, then the second awk will a buffer full of data to process. Until then, nothing will happen.
You start the command with tail -f, that keeps the output open and therefore does not send a needed newline to the other commands.
This works perfectly fine:
cat log | awk '{if (NF>3) {print $1}; }' | grep 64
So, the problem is buffering. The middle awk is doing normal buffering instead of interactive buffering. This works (non-portably) with mawk:
tail -f log | mawk -W interactive '{if (NF>3) {print $1}; }' | awk '{print}'
You could read GNU description of the issue.
In any case, just check that the awk used in the middle could be told to buffer interactively.
Added:
The command system("") seems to unblock the buffering. It is POSIX, but does not work with mawk.
tail -f log | awk '{if (NF>3) {print $1}; system("")}' | awk '{print}'
search for "parallel --pipe" in the link to avoid the buffering
https://www.gnu.org/software/parallel/parallel_tutorial.html
Something like this will hang:
tail -f textfile | awk '{print $0}'
while grep won't hang when used instead of awk.
My actual intention is to add color to some log output using merely standard commands; however it seems that piping tail -f into awk won't work. I don't know if it's a buffer problem, but I tried some approaches that haven't worked, like:
awk '{print $0;fflush()}'
and also How to pipe tail -f into awk
Any ideas?
I ran into almost exactly the same problem with mawk. I think it is due to the way mawk is flushing its buffer, the problem went away when I switched to gawk. Hope this helps (a bit late I know).
I tried this command :
tail -f test | awk '{print $0;}'
And it doesn't hang. Awk will print the new values each time I add something in the test file.
echo "test" >> test
I think you just forgot a quote in your command because you wrote (edit : well, before your post was edited) :
tail -f textfile | awk {print $0}'
Instead of :
tail -f textfile | awk '{print $0}'
I need to assign the output of a command to a variable. The command I tried is:
grep UUID fstab | awk '/ext4/ {print $1}' | awk '{print substr($0,6)}'
I try this code to assign a variable:
UUID=$(grep UUID fstab | awk '/ext4/ {print $1}' | awk '{print substr($0,6)}')
However, it gives a syntax error. In addition I want it to work in a bash script.
The error is:
./upload.sh: line 12: syntax error near unexpected token ENE=$( grep UUID fstab | awk '/ext4/ {print $1}' | awk '{print substr($0,6)}'
)'
./upload.sh: line 12: ENE=$( grep UUID fstab | awk '/ext4/ {print $1}' | awk '{print substr($0,6)}'
)'
well, using the '$()' subshell operator is a common way to get the output of a bash command. As it spans a subshell it is not that efficient.
I tried :
UUID=$(grep UUID /etc/fstab|awk '/ext4/ {print $1}'|awk '{print substr($0,6)}')
echo $UUID # writes e577b87e-2fec-893b-c237-6a14aeb5b390
it works perfectly :)
EDIT:
Of course you can shorten your command :
# First step : Only one awk
UUID=$(grep UUID /etc/fstab|awk '/ext4/ {print substr($1,6)}')
Once more time :
# Second step : awk has a powerful regular expression engine ^^
UUID=$(cat /etc/fstab|awk '/UUID.*ext4/ {print substr($1,6)}')
You can also use awk with a file argument ::
# Third step : awk use fstab directlty
UUID=$(awk '/UUID.*ext4/ {print substr($1,6)}' /etc/fstab)
Just for trouble-shooting purposes, and something else to try to see if you can get this to work, you could also try to use "backticks", e.g,
cur_dir=`pwd`
would save the output of the pwd command in your variable cur_dir, though using $() approach is generally preferable.
To quote from a pages given to me on http://unix.stackexchange.com:
The second form `COMMAND` (using backticks) is more or less obsolete for Bash, since it
has some trouble with nesting ("inner" backticks need to be escaped)
and escaping characters. Use $(COMMAND), it's also POSIX!