I've got a bash script accepting several files as input which are mixed with various script's options, for example:
bristat -p log1.log -m lo2.log log3.log -u
I created an array where i save all the index where i can find files in the script's call, so in this case it would be an arrat of 3 elements where
arr_pos[0] = 2
arr_pos[1] = 4
arr_pos[3] = 5
Later in the script I must call "head" and "grep" in those files and i tried this way
head -n 1 ${arr_pos[0]}
but i get this error non runtime
head: cannot open `2' for reading: No such file or directory
I tried various parenthesis combinations, but I can't find which one is correct.
The problem here is that ${arr_pos[0]} stores the index in which you have the file name, not the file name itself -- so you can't simply head it. The array storing your arguments is given by $#.
A possible way to access the data you want is:
#! /bin/bash
declare -a arr_pos=(2 4 5)
echo ${#:${arr_pos[0]}:1}
Output:
log1.log
The expansion ${#:${arr_pos[0]}:1} means you're taking the values ranging from the index ${arr_pos[0]} in the array $#, to the element of index ${arr_pos[0]} + 1 in the same array $#.
Another way to do so, as pointed by #flaschenpost, is to eval the index preceded by $, so that you'd be accessing the array of arguments. Although it works very well, it may be risky depending on who is going to run your script -- as they may add commands in the argument line.
Anyway, you may should try to loop through the entire array of arguments by the beginning of the script, hashing the values you find, so that you won't be in trouble while trying to fetch each value later. You may loop, using a for + case ... esac, and store the values in associative arrays.
I think eval is what you need.
#!/bin/bash
arr_pos[0]=2;
arr_pos[1]=4;
arr_pos[2]=5;
eval "cat \$${arr_pos[1]}"
For me that works.
Related
I'm trying to write a simple script that creates five textfiles enumerated by a variable in a loop. Can anybody tell my how to make the arithmetic expression be evaluated. This doesn't seem to work:
touch ~/test$(($i+1)).txt
(I am aware that I could evaluate the expression in a separate statement or change of the loop...)
Thanks in advance!
The correct answer would depend on the shell you're using. It looks a little like bash, but I don't want to make too many assumptions.
The command you list touch ~/test$(($i+1)).txt will correctly touch the file with whatever $i+1 is, but what it's not doing, is changing the value of $i.
What it seems to me like you want to do is:
Find the largest value of n amongst the files named testn.txt where n is a number larger than 0
Increment the number as m.
touch (or otherwise output) to a new file named testm.txt where m is the incremented number.
Using techniques listed here you could strip the parts of the filename to build the value you wanted.
Assume the following was in a file named "touchup.sh":
#!/bin/bash
# first param is the basename of the file (e.g. "~/test")
# second param is the extension of the file (e.g. ".txt")
# assume the files are named so that we can locate via $1*$2 (test*.txt)
largest=0
for candidate in (ls $1*$2); do
intermed=${candidate#$1*}
final=${intermed%%$2}
# don't want to assume that the files are in any specific order by ls
if [[ $final -gt $largest ]]; then
largest=$final
fi
done
# Now, increment and output.
largest=$(($largest+1))
touch $1$largest$2
I have x files: A, B, C... What I need to do is pass each of these files as the first command line argument to a python file and pass the others as the second command line argument until all files have been passed as $1 once. For example, on the first iteration A is $1 and B,C... is $2. On the second iteration, B is $1 and A,C... is $2. I've read about the shift command in shell but am not very sure if it will work in my case (I'm also relatively new to shell scripting). Also, is there a limit to the number of command line arguments I can pass to my python script? I would also like to create a variable to hold the list of file names before iterating through my files. Thank you!
Bash has arrays, and supports array slicing via ${array[#]:start:end} syntax, where start and end are optional indices. That's enough to get the job done.
#!/bin/bash
# Store the master list of file names in an array called $files.
files=("$#")
for ((i = 0; i < ${#files[#]}; ++i)); do
# Store the single item in $file and the rest in an array $others.
file=${files[i]}
others=("${files[#]:0:i}" "${files[#]:i+1}")
# Run command.py. Use ${others[*]} to concatenate all the file names into one long
# string, and override $IFS so they're joined with commas.
(IFS=','; command.py "${files[i]}" "${others[*]}")
done
I have a bash script that take advantage of a local toolbox to perform an operation
my question is fairly simple
I have multiple files that are the same quantities but different time steps i would like to first untar them all, and then use the toolbox to perform some manipulation but i am not sure if i am on the right track.
=============================================
The file is as follows
INPUTS
fname = a very large number or files with same name but numbering
e.g wnd20121.grb
wnd20122.grb
.......
wnd2012100.grb
COMMANDS
> cdo -f nc copy fname ofile(s)
(If this is the ofile(s)=output file how can i store it for sequent use ? Take the ofile (output file) from the command and use it / save it as input to the next, producing a new subsequent numbered output set of ofile(s)2)
>cdo merge ofile(s) ofile2
(then automatically take the ofile(s)2 and input them to the next command and so on, producing always an array of new output files with specific set name I set but different numbering for distinguishing them)
>cdo sellon ofile(s)2 ofile(s)3
------------------------------------
To make my question clearer, I would like to know the way in which I can instruct basically through a bash script the terminal to "grab" multiple files that are usually the same name but have a different numbering to make the separate their recorded time
e.g. file1 file2 ...file n
and then get multiple outputs , with every output corresponding to the number of the file it converted.
e.g. output1 output2 ...outputn
How can I set these parameters so the moment they are generated they are stored for subsequent use in the script, in later commands?
Your question isn't clear, but perhaps the following will help; it demonstrates how to use arrays as argument lists and how to parse command output into an array, line by line:
#!/usr/bin/env bash
# Create the array of input files using pathname expansion.
inFiles=(wnd*.grb)
# Pass the input-files array to another command and read its output
# - line by line - into a new array, `outFiles`.
# The example command here simply prepends 'out' to each element of the
# input-files array and outputs each (modified) element on its own line.
# Note: The assumption is that the filenames have no embedded newlines
# (which is usually true).
IFS=$'\n' read -r -d '' -a outFiles < \
<(printf "%s\n" "${inFiles[#]}" | sed s'/^/out-/')
# Note: If you use bash 4, you could use `readarray -t outFiles < <(...)` instead.
# Output the resulting array.
# This also demonstrates how to use an array as an argument list
# to pass to _any_ command.
printf "%s\n" "${outFiles[#]}"
I'm dealing with a pipeline of predominantly shell and Perl files, all of which pass parameters (paths) to the next. I decided it would be better to use a single file to store all the paths and just call that for every file. The issue is I am using awk to grab the files at the beginning of each file, and it's turning out to be a lot of repetition.
My question is: I do not know if there is a way to store key-value pairs in a file so shell can natively do something with the key and return the value? It needs to access an external file, because the pipeline uses many scripts and a map in a specific file would result in parameters being passed everywhere. Is there some little quirk I do not know of that performs a map function on an external file?
You can make a file of env var assignments and source that file as need, ie.
$ cat myEnvFile
path1=/x/y/z
path2=/w/xy
path3=/r/s/t
otherOpt1="-x"
Inside your script you can source with either . myEnvFile or the more versbose version of the same feature sourc myEnvFile (assuming bash shell) , i.e.
$cat myScript
#!/bin/bash
. /path/to/myEnvFile
# main logic below
....
# references to defined var
if [[ -d $path2 ]] ; then
cd $path2
else
echo "no pa4h2=$path2 found, can't continue" 1>&1
exit 1
fi
Based on how you've described your problem this should work well, and provide a-one-stop-shop for all of your variable settings.
IHTH
In bash, there's mapfile, but that reads the lines of a file into a numerically-indexed array. To read a whitespace-separated file into an associative array, I would
declare -A map
while read key value; do
map[$key]=$value
done < filename
However this sounds like an XY problem. Can you give us an example (in code) of what you're actually doing? When I see long piplines of grep|awk|sed, there's usually a way to simplify. For example, is passing data by parameters better than passing via stdout|stdin?
In other words, I'm questioning your statement "I decided it would be better..."
I have one loop that creates a group of variables like DISK1, DISK2... where the number at the end of the variable name gets created by the loop and then loaded with a path to a device name. Now I want to use those variables in another loop to execute a shell command, but the variable doesn't give its contents to the shell command.
for (( counter=1 ; counter<=devcount ; counter++))
do
TEMP="\$DISK$counter"
# $TEMP should hold the variable name of the disk, which holds the device name
# TEMP was only for testing, but still has same problem as $DISK$counter
eval echo $TEMP #This echos correctly
STATD$counter=$(eval "smartctl -H -l error \$DISK$counter" | grep -v "5.41" | grep -v "Joe")
eval echo \$STATD$counter
done
Don't use eval ever, except maybe if there is no other way AND you really know what you are doing.
The STATD$counter=$(...) should give an error. That's not a valid assignment because the string "STATD$counter" is not a valid variable name. What will happen is (using a concrete example, if counter happened to be 3 and your pipeline in the $( ) output "output", bash will only expand that line as far as "STATD3=output" so it will try to find a command named "STATD3=output" and run it. Odds are this is not what you intended.
It sounds like everything you want to do can be accomplished with arrays instead. If you are not familiar with bash arrays take a look at Greg's Wiki, in particular this page or the bash man page to find out how to use them.
For example, in the loop you didn't post in your question: make disk (not DISK: don't use all upper case variable names) an array like so
disk+=( "new value" )
or even
disk[counter]="new value"
Then in the loop in your question, you can make statd an array as well and assign it with values from disk by
statd[counter]="... ${disk[counter]} ..."
It's worth saying again: avoid using eval.