Use Bash to Read a File and Then Execute a Command from the Words Extracted

Use bash to read a file and then execute a command from the words extracted

You can use the "for" loop to do this. something like..

for WORD in `cat FILE`
do
   echo $WORD
   command $WORD > $WORD
done

How to execute commands read from the txt file using shell?

A file with one valid command per line is itself a shell script. Just use the . command to execute it in the current shell.

$ echo "pwd" > temp.txt
$ echo "ls" >> temp.txt
$ . temp.txt

Extract all the words from a text file in bash

Maybe, something like that:

WORDS=$(grep -o -E "(\w|')+" words.txt | sed -e "s/'.*\$//" | sort -u -f)

UPDATE

Explanations:

• var=$(...command...) : Execute command (newer and better solution than `...command...`) and put standard output to var variable
• grep -o -E "(\w|')+" words.txt : Read file words.txt and apply grep filter
  
  • grep filter is : print only found tokens (-o) from extended (-E) rational expression (\w|')+. This expression is form extract characters of words (\w : synonym of [_[:alnum:]], alnum is for alpha-numeric characters like [0-9a-zA-Z] for english/american but extended to many other characters for other languages) or (|) simple cote ('), one or more times (+) : see man grep
• The standard ouptut of grep is the standard input of next command sed with the pipe (|)
• sed -e "s/'.*\$//" : Execute (-e) expression s/'.*\$// :
  
  • sed expression is substitution (s/) of '.*\$ (simple cote followed by zero or any characters to the end of line) by empty string (between the last two slashes (//)) : see man sed
• The standard ouptut of sed is the standard input of next command sort with the pipe (|)
• sort the result of sed and remove doubles (-u : uniq) and do not make a differences between upper and lower characters (case) : see man sort

Shell script to execute command on each line of a file with space-delimited fields

Use read and a while loop in bash to iterate over the file line-by-line and call wget on each iteration:

while read -r NAME URL; do wget "$URL" -o "$NAME"; done < File.txt

How to read file and extract particular data in shell script?

You can use one liner such as awk or simplify by breaking into different commands.
First filter your

if [ -n "$1" ]; then 
    line=`grep $1 sltconfig.cfg |head -1`
    param=`echo line | awk -F'=' '{print $2}'`
    python /medaff/Scripts/python/iMedical_Consumption_load_Procs.py "${param}"
else
    echo "Pass the application name as argument"
fi

Is it possible to start while read a file that is currently being written? (and will the entirety of the file be read?)

read operates incrementally, a character at a time. It won't care whether a line is available in a file until it actually tries to read that specific line.

Thus, if your writer is writing and actually flushing its buffers faster than your reader reads, and appending to the same file in-place (rather than following a write-and-rename pattern), a reader won't know or care that content wasn't available yet when it first started execution.

extract words from a file

You could use grep:

• -E '\w+' searches for words
• -o only prints the portion of the line that matches

% cat temp
Some examples use "The quick brown fox jumped over the lazy dog,"
rather than "Lorem ipsum dolor sit amet, consectetur adipiscing elit"
for example text.
# if you don't care whether words repeat
% grep -o -E '\w+' temp
Some
examples
use
The
quick
brown
fox
jumped
over
the
lazy
dog
rather
than
Lorem
ipsum
dolor
sit
amet
consectetur
adipiscing
elit
for
example
text

If you want to only print each word once, disregarding case, you can use sort

• -u only prints each word once
• -f tells sort to ignore case when comparing words

# if you only want each word once
% grep -o -E '\w+' temp | sort -u -f
adipiscing
amet
brown
consectetur
dog
dolor
elit
example
examples
for
fox
ipsum
jumped
lazy
Lorem
over
quick
rather
sit
Some
text
than
The
use

Read a file line by line assigning the value to a variable

The following reads a file passed as an argument line by line:

while IFS= read -r line; do
    echo "Text read from file: $line"
done < my_filename.txt

This is the standard form for reading lines from a file in a loop. Explanation:

• IFS= (or IFS='') prevents leading/trailing whitespace from being trimmed.
• -r prevents backslash escapes from being interpreted.

Or you can put it in a bash file helper script, example contents:

#!/bin/bash
while IFS= read -r line; do
    echo "Text read from file: $line"
done < "$1"

If the above is saved to a script with filename readfile, it can be run as follows:

chmod +x readfile
./readfile filename.txt

If the file isn’t a standard POSIX text file (= not terminated by a newline character), the loop can be modified to handle trailing partial lines:

while IFS= read -r line || [[ -n "$line" ]]; do
    echo "Text read from file: $line"
done < "$1"

Here, || [[ -n $line ]] prevents the last line from being ignored if it doesn't end with a \n (since read returns a non-zero exit code when it encounters EOF).

If the commands inside the loop also read from standard input, the file descriptor used by read can be chanced to something else (avoid the standard file descriptors), e.g.:

while IFS= read -r -u3 line; do
    echo "Text read from file: $line"
done 3< "$1"

(Non-Bash shells might not know read -u3; use read <&3 instead.)

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