I am new to awk.I just try to write some thing that to exchange my text file.but I failed.
I want to output like 'hello'.
I used command awk '{print "'hello'"}' filename to do it.but failed:
output like: hello
but I used command awk '{print "\'hello\'"}' filename to do it.failed again:
output like: >
ok.it seems that the awk command do not get what I mean.
So I am confused about that .how to solve the problem.
guys thanks.
Using the ascii code:
awk '{print "\x27" "hello" "\x27"}' filename
Using a variable:
awk -v q="'" '{print q "hello" q}' filename
Example:
$ seq 2 > filename
$ awk '{print "\x27" "hello" "\x27"}' filename
'hello'
'hello'
$ awk -v q="'" '{print q "hello" q}' filename
'hello'
'hello'
Simply use double quotes:
awk "{print \"'hello'\"}" filename
Although that won't really modify your file.
awk '{print "'"'"'hello'"'"'"}' filename
clyfish's answer works, if you must have it output single quotes and you must use scripts that you pass on the command line.
What I usually do in cases like these, though, when I need to do quoting but I don't want to write a 'real' awk script, is this:
awk 'function q(word) { return "\"" word "\"" }
{ printf("mv %s SomeDir/;", q($0)) }'
What I've done is to define a function that returns whatever you pass it in double quotes. Then use printf to actually use it. Without doing that, I would have had to do:
awk '{ print("mv \"" $0 "\" SomeDir/;") }';
It gets pretty nasty. For more complicated examples, this can be a life saver.
However, suppose you really do need to output something with actual single quotes. In that case dealing with odd shell quoting rules while trying to pass scripts like this on the command line is going to drive you completely insane, so I would suggest you just write a simple throwaway file.
#!/usr/bin/awk
# hi.awk
{ print("'hello'") }
then call it:
awk -f ./hi.awk
You don't really even need the #! line in the file if you do it that way, but neither does it hurt.
Related
I currently have the following line of code:
ls /some/dir/prefix* | sed -e 's/prefix.//' | tr '\n' ' '
Which does achieve what I want it to do:
Get list of files starting with prefix
Remove path and prefix from each string
Remove newlines and replace with spaces for later processing.
For example:
/some/dir/prefix.hello
/some/dir/prefix.world
Should become
hello world
But I feel like there's a nicer way of doing this. Is there a better way to do this in one line?
Here is a two-liner using just built-ins that does it:
fnames=(some/dir/prefix*)
echo "${fnames[#]##*.}"
And here's how this works:
fnames=(some/dir/prefix*) creates an array with all the files starting with prefix and avoids all the problems that come with parsing ls
echo "${fnames[#]##*.}" is a combination of two parameter expansions: ${fnames[#]} prints all array elements, and the ##*. part removes the longest match of anything that ends with . from each array element, leaving just the extension
If you're hell-bent on a one-liner, just join the two commands with &&.
passing ls output to external programs is not recommended, following bash solution may help you here.
for file in prefix*; do echo ${file##*.}; done
Adding a non-one liner form of solution too now.
for file in prefix*
do
echo ${file##*.}
done
Here is a very simple Awk one-liner to achieve this :
awk -F. '{$0=FILENAME; printf $NF" "; nextfile}' /some/dir/prefix*
It essentially does the following :
-F.: Set the field separator FS to a .. This way $NF represents the extension.
$0=FILENAME: Ignore the current record and set it to FILENAME, reparse everything this way.
print $NF; nextfile : print the extension and go to the next file.
The problem with this is that the file still reads a record of the current file. If that file is empty this will fail.
To make this work with empty files, you could use the gawk extension BEGINFILE
awk -F. 'BEGINFILE{$0=FILENAME; printf $NF" "; nextfile}' /some/dir/prefix*
Or you can loop over all the arguments :
awk -F. 'BEGIN{for(i in ARGV){$0=ARGV[i]; printf $NF" "};exit}' /some/dir/prefix*
One approach with awk:
ls /some/dir/prefix* | awk -F"." '{printf "%s ", $2} END {print ""}'
It might qualify as being "nicer" because there's only one command the output is piped through?!
Does awk support using a different delimiter character than ' in print? e.g. Instead of awk '{print $1}', something like awk -d # #{print $1}#
I was actually looking at the C source code and it's a pretty short program; is there an alternative version that allow that?
It can't: The ' isn't passed to awk; instead, it's understood by the shell itself. Thus, when you run awk '{print $1}', what you're actually calling at the OS level is something like:
/* this is C syntax, so the double-quotes are C quotes; only their contents are literal */
execvp("awk", { "awk", "{print $1}", NUL });
Notably, the single-quotes aren't there at all any more -- they were parsed out by the shell when it understood them as instructions for how it should break the command into an argument list.
To see it in another way, consider if you put your script in a separate file and called
awk -f my.awk
The contents of my.awk would simply be
{print $1}
not
'{print $1}'
The single quotes are only used by the shell to ensure that the script is passed literally to awk, rather than being subject to any particular shell processing that could change the script before awk could read it.
I'm on a Mac, and I want to find a field in a CSV file adjacent to a search string
This is going to be a single file with a hard path; here's a sample of it:
84:a5:7e:6c:a6:b0, AP-ATC-151g84
84:a5:7e:6c:a6:b1, AP-A88-131g84
84:a5:7e:73:10:32, AP-AG7-133g56
84:a5:7e:73:10:30, AP-ADC-152g81
84:a5:7e:73:10:31, AP-D78-152e80
so if my search string is "84:a5:7e:73:10:32"
I want to get returned "AP-AG7-133g56"
I had been working within an Applescript, but maybe a shell script will do.
I just need the proper syntax for opening the file and having awk search it. Again, I'm weak conceptually on how shell commands run, how they must be executed, etc
This errors, gives me ("command not found"):
set the_file to "/Users/Paw/Desktop/AP-Decoder 3.app/Contents/Resources/BSSIDtable.csv"
set the_val to "70:56:81:cb:a2:dc"
do shell script "'awk $1 ~ the_val {print $2} the_file'"
Thank you for coddling me...
This is a relatively simple:
awk '$1 == "70:56:81:cb:a2:dc," {print "The answer is "$2}' 'BSSIDtable.csv'
(the "The answer is " text can be omitted if you only wish to see only the data, but this shows you how to get more user-friendly output if desired).
The comma is included since awk uses white space for separators so the comma becomes part of column 1.
If the thing you're looking for is in a shell variable, you can use -v to provide that to awk as an awk variable:
lookfor="70:56:81:cb:a2:dc,"
awk -v mac=$lookfor '$1 == mac {print "The answer is "$2}' 'BSSIDtable.csv'
As an aside, your AppleScript solution is probably not working because the $1/$2 are being interpreted as shell variable rather than awk variables. If you insist on using AppleScript, you will have to figure out how to construct a shell command that quotes the awk commands correctly.
My advice is to just use the shell directly, the number of people proficient in that almost certainly far outnumber those proficient in AppleScript :-)
if sed is available (normaly on mac, event if not tagged in OP)
simple but read all the file
sed -n 's/84:a5:7e:73:10:32,[[:blank:]]*//p' YourFile
quit after first occurence (so average of 50% faster on huge file)
sed -n -e '/84:a5:7e:73:10:32,[[:blank:]]*/!b' -e 's///p;q' YourFile
awk
awk '/^84:a5:7e:73:10:32/ {print $2}'
# OR using a variable for batch interaction
awk -v Src='84:a5:7e:73:10:32' '$1 == Src {print $2}'
# OR assuming that case is unknow
awk -v Src='84:a5:7e:73:10:32' 'BEGIN{IGNORECASE=1} $1 == Src {print $2}'
by default it take $0 as compare test if a regex is present, just add the ^ to take first field content
I have a shell script that constructs an awk program as a string then pass that string to awk. This is because I want to use values of shell variables in the awk program.
My code looks like this:
awk_prog="'{if (\$4~/$shell_var/) print \$1,\$2}'"
echo $awk_prog
awk $awk_prog $FILENAME
However, when I pass the string to awk, I always get the error:
'{if ($4~/regex/) print $1,$2}'
awk: '{if
awk: ^ invalid char ''' in expression
What does that error message mean? I tried the -F: switch but it does not help. How can I settle this issue?
Thank you.
This is caused by shell quoting. The following will work:
awk_prog="{ if (\$4 ~ /$shell_var/) print \$1, \$2 }"
echo "$awk_prog"
awk "$awk_prog" $FILENAME
When you run awk '{ print }' foo from the command line, the shell interprets and removes the quotes around the program so awk receives two arguments - the first is the program text and the second is the filename foo. Your example was sending awk the program text '{if ...}' which is invalid syntax as far as awk is concerned. The outer quotes should not be present.
In the snippet that I gave above, the shell uses the quotes in the awk_prog= line to group the contents of the string into a single value and then assigns it to the variable awk_prog. When it executes the awk "$awk_prog"... line, you have to quote the expansion of $awk_prog so awk receives the program text as a single argument.
There's another way to get your shell variable into awk -- use awk's -v option:
awk -v pattern="$shell_var" '$4 ~ pattern {print $1, $2}' "$FILENAME"
Use -v multiple times if you have several variables to pass to awk.
If you truly want to hold your awk program in a shell variable, build it up using printf:
awk_script="$( printf '$4 ~ /%s/ {print $1, $2}' "$shell_var" )"
awk "$awk_script" "$FILENAME"
Note the use of quotes in the printf command: single quotes around the template to protect the dollar signs you want awk to interpret, double quotes for shell variables.
Another (IMO simpler) solution which (I think) addresses what you are intuitively trying to do is simply to use eval. You want the shell to behave as if you had literally typed:
awk '{if ($4~/foo/) print $1,$2}' path
(where foo and path are the literal contents of $shell_var and $FILENAME). To make that happen, just slap an eval on the front of your last line (and perhaps quotes for good measure, but they aren't necessary in this case) so that your last line is:
eval "awk $awk_prog $FILENAME"
I have a file with fields separated by pipe characters and I want to print only the second field. This attempt fails:
$ cat file | awk -F| '{print $2}'
awk: syntax error near line 1
awk: bailing out near line 1
bash: {print $2}: command not found
Is there a way to do this?
Or just use one command:
cut -d '|' -f FIELDNUMBER
The key point here is that the pipe character (|) must be escaped to the shell. Use "\|" or "'|'" to protect it from shell interpertation and allow it to be passed to awk on the command line.
Reading the comments I see that the original poster presents a simplified version of the original problem which involved filtering file before selecting and printing the fields. A pass through grep was used and the result piped into awk for field selection. That accounts for the wholly unnecessary cat file that appears in the question (it replaces the grep <pattern> file).
Fine, that will work. However, awk is largely a pattern matching tool on its own, and can be trusted to find and work on the matching lines without needing to invoke grep. Use something like:
awk -F\| '/<pattern>/{print $2;}{next;}' file
The /<pattern>/ bit tells awk to perform the action that follows on lines that match <pattern>.
The lost-looking {next;} is a default action skipping to the next line in the input. It does not seem to be necessary, but I have this habit from long ago...
The pipe character needs to be escaped so that the shell doesn't interpret it. A simple solution:
$ awk -F\| '{print $2}' file
Another choice would be to quote the character:
$ awk -F'|' '{print $2}' file
Another way using awk
awk 'BEGIN { FS = "|" } ; { print $2 }'
And 'file' contains no pipe symbols, so it prints nothing. You should either use 'cat file' or simply list the file after the awk program.