simple bash script to write to a file

[newsman]

ha i need help. I have tried lots of different ways but the most successful (and yet not a success) is as follows


#!/bin/bash
#A script that takes two arguments, a line of text and a filename
#and adds to the file of filename with the line of text at the bigenning.

if [$# -eq 2]
then if [ -f $2 ]
then vi +I%s'$1'+'wq' $2;
fi
else
echo "usage script text filname";
fi
exit 0


The following is output:


newsman@newsman-laptop:~$sh firstline3 "hello my name is newsman" textlines
firstline3: 11: [2: not found
usage script text filname
newsman@newsman-laptop:~$ sh firstline3
firstline3: 11: [0: not found
usage script text filname

[Tuna-Fish]

The basics are:
echo $2 | cat - $1 > temp
mv temp $1

although you need really robust naming for temp, like:

TEMPNAME="/tmp/`whoami``date +%s%N`myshellscript"
echo $2 | cat - $1 > $TEMPNAME
mv $TEMPNAME $1

Is it ugly? oh yes. But it works. Also, wrap in proper tests for the existence of file etc.

[ghostdog74]

ha i need help. I have tried lots of different ways but the most successful (and yet not a success) is as follows


#!/bin/bash
#A script that takes two arguments, a line of text and a filename
#and adds to the file of filename with the line of text at the bigenning.

if [$# -eq 2]
then if [ -f $2 ]
then vi +I%s'$1'+'wq' $2;
fi
else
echo "usage script text filname";
fi
exit 0




....
then
sed -i "1i $1" file
....

[newsman]

cannot use sed or temporary files (> operator). not fair la

on second check, i am allowed to use > operator and temporary files

[newsman]

I completed this exercise, next one is to insert line at the middle. I know i can use wc -l command to find out the lines, but it also displays the filename. Is there a better way without using sed or awk? Thanks. Following that is an exercise to append a file without using temporary files (the only time when I am not allowed using temporary files), display user permissions of certain file and display processes. I think apart from the not using temp file clause the rest should be straight forward.

[newsman]

I completed the first exercise, ( i managed to complete it using call to vim).

The second ex is to insert line at the middle of the file is proving too difficult.

The third one i managed to complete somehow (i can't believe i did that without any help! yippeee but i used a call to vim with script again.) (the exercise was to gather env variable and grep them with username and format them so that instead of line number: ..... you get line number)


the fourth i have attempted a thousand million times, I am now confused with BASH and variable assingment. Particularly assigning strings . The point is to check file ownership and instead of printing rw..... string format into columns Read Write Execute followed by three rows for Owner, Group and Everyone respectively and have yes or no for each.

Please let me know of any good tutorial or point to me what is going on in this code which makes it not work. Thanks

#!/bin/bash
STR="Hello World"
touch output01;
ls -l temp01 > output01;
cat output01 > $STR;
echo $STR;

I have tried to use pipe operator instead of > and i get error.

Even if i get read of dollar sign, in cat > $STR statement, still no assignment occurs.


The fifth is similar to this i guess i have to collect process and produce a similar formatted output.

These exercises really hit home the power of awk and sed right. Too bad I can't use them for these exercises. Another thing is on formatting output. Any pointer would be appreciated.

[RIchard James13]

Please let me know of any good tutorial or point to me what is going on in this code which makes it not work. Thanks

At the Linux Documentation Project (http://tldp.org/) is the Advanced BASH Scripting Guide (http://tldp.org/LDP/abs/html/index.html)

Although not a tutorial it is a good reference especially if you look at the examples.

cat output01 > $STR;
This line won't work because you can't redirect straight to a variable.
look on the bottom of this page (http://tldp.org/LDP/abs/html/varassignment.html) for some ways to do it.

[newsman]

howcome this does not work in the script but works in the prompt?

$ EXCLAIM=cowabunga
$ echo ${EXCLAIM:0:3}
cow
$ echo ${EXCLAIM:3:7}
abunga

If I were to have these echo lines in script i would get:
Syntax error: Bad substitution

[newsman]

Is there another way to look at cells in a row of text (delimited by tab or : or something)?

[newsman]

oh man just solved another piece of the puzzle..i will try to get a webpage to document all my coding.. but not before the work is done... but now i have a variable $STR with following user1 user2 user3 user4 user5 (space delimited list)..how can i turn this into a an array in bash

[newsman]

I have file

with random names seperated by space, duplicate names are side by side (sorted out). i want to pass them to "ps -u" function one by one..

so far i have
#!/bin/bash
#STR=$(users)
#VAR=$(finger | wc -l)


#STR2=${STR#*" "}
VAR2=$(cat users);

#echo output of users $STR
#VAR=$(($VAR-1))
echo $VAR
#echo $STR2
echo $VAR2
NUM=10;

VARl3=${VAR2##*" "} #get the last name

while [$NUM -gt 0]
do
echo $VARl3 # perform ps

while [$VARn -ne $VARc] #continue shortening the string until unique name found
do
VARn=${VAR2%" "*} #new string
Number=$(($UM-1))
#echo $VAR4
VARc=${VARm##*" "} #get second last name
done
VARl3=$VARc
done

and output




john.smith john.smith william.shakespear william.shakespear whocares.whoevever
userprocesses: 30: [10: not found

[mssever]

while [$NUM -gt 0]

You need spaces around [ and ]. Also, if you use [[ ]] instead of [ ], you'll find that it supports a few more options and is less likely to break in weird ways.

[newsman]

I am getting errors when i try to use functions in bash

#!/bin/bash

VAR=$(cat users)
NUM=10

function getname(){
LAST=${VAR##*" "}
VAR=${VAR%" "*} #new string
NUM=$(($NUM-1))
}

function printout(){
echo $LAST
echo $NUM
echo new string $VAR

}

while [ $NUM -gt 0 ]
do
$(getname())
$(printout())


done
output
userprocesses4: 6: Syntax error: "(" unexpected


even if i had empty functions i am getting this error in BASH?

I am also having trouble testing for string equality

if [ test $LAST=$LASTl ]
then
{
VAR=${VAR%" "*} #new string
NUM=$(($NUM-1))
LAST=${VAR##*" "}
}
else
{
echo $LAST
VAR=${VAR%" "*} #new string
echo new string $VAR
NUM=$(($NUM-1)) #decrement number of users
LASTl=$LAST
LAST=${VAR##*" "}
echo $NUM
}
fi

results in

[: 33: adul.latif1=abdul.latif1: unexpected operator

[howlingmadhowie]

here a simple function to get you started:


#!/bin/bash

function myfunc {
echo "hello world!"
echo $1
}

myfunc 3

[mssever]

I am getting errors when i try to use functions in bash
Either of the following will work, but they can't be combined: function foo {
#do stuff
}

bar() {
#do more stuff
}I prefer the first form because it doesn't imply that you can place arguments inside the parentheses (since you can't).

EDIT:
if [ test $LAST=$LASTl ]Try if [[ "$LAST" = "$LASTl" ]][ and test mean the same thing; don't use both. [[ is safer than [. Make it a habit to always enclose your variables in double quotes. It will save a lot of headaches later.

[newsman]

I get an error on that as well

myfunc1: 3: function: not found
hello world!

myfunc1: 6: Syntax error: "}" unexpected

[newsman]

I will do half an hour more brain squeezing before i get back....

[howlingmadhowie]

I get an error on that as well

myfunc1: 3: function: not found
hello world!

myfunc1: 6: Syntax error: "}" unexpected


are you sure you entered my example correctly? it looks okay to me.

[newsman]

my idea was to use recursive functioning to test for uniqueness (until unique name found call the function to shorten string of names and get new names and check)

but i managed to complete without functions (i am a big fan of the KISS principle although I think i better practice this before progressing in my application)



#!/bin/bash

VAR=$(cat users)
echo $VAR
NUM=11

LAST=${VAR##*" "}
NUM=$(($NUM-1))
#VAR=${VAR%" "*} #new string


echo $NUM
LASTl="anything"

while [ $NUM -gt 0 ]
do
if [ "$LAST" = "$LASTl" ]
then
{
VAR=${VAR%" "*} #new string
NUM=$(($NUM-1))
echo $NUM
LAST=${VAR##*" "}
}
else
{
echo $LAST
VAR=${VAR%" "*} #new string
echo new string $VAR
NUM=$(($NUM-1)) #decrement number of users
LASTl=$LAST
LAST=${VAR##*" "}
echo $NUM
}
fi

done


thanks a bunch guys

Also when i place [[ instead of [ in if [ "$LAST" = $LASTl" ] i get an error
userprocesses5: 37: [[: not found

now i have to submit in little under three hours and hopefully the evaluators wll accept my work, so happy, if you were in bradford i could treat you.

my function i typed
#!/bin/bash

function myfunc {
echo "hello world!"
echo $1
}

myfunc 3
I just copied and pasted just now to make sure..got the same error

[mssever]

Dunno if it's too late, but here are a couple more tips:


For recursive functions, be absolutely sure to declare all variables as local. Otherwise, Bad Things will happen. E.g.: function adder {
local current="$1"
local max="$2"
[[ "$current" -ge "$max" ]] && return current
(($current++))
adder "$current" "$max"
}
echo "$(adder 0 10)"
[[ is a Bash extension. If you're not calling bash (or if you're calling Bash, but as sh), then it might not work. In particular, /bin/sh actually calls dash, not bash on Ubuntu. [[ doesn't work in dash.
If you must use [, consider that an empty string will cause errors, even with quotes. Compare strings with something added, e.g., [ "x$foo" = "x$bar" ] && echo "Success"

[newsman]

actually i do have time but, i have few loose ends to tie up.. i have to answers questions on use of vi...use date function to append to file and submit that file and this particular example... i have to get VAR initially to read from output of users command and num to read from finger | wc -l (and decrement initial value by one since finger results in one extra header line) to find uers and instead of echoing names, i have to run ps -u $LAST command on them...i will probably spend an hour more on this and then try to tie up other loose ends

[howlingmadhowie]

my function i typed
#!/bin/bash

function myfunc {
echo "hello world!"
echo $1
}

myfunc 3
I just copied and pasted just now to make sure..got the same error

that's weird. it works fine for me. let me think...

[mssever]

that's weird. it works fine for me. let me think...

function foo is a Bashism. The portable way is foo(). This and the OP's trouble with [[ (another Bashism) suggests to me that he/she isn't actually using Bash.

[newsman]

is there any way to confirm but it looks like the case..

i did a search on yahoo "bash or dash" and found this in http://ubuntuforums.org/archive/index.php/t-221769.html

i thought this means both bash and dash are available in and i need to have the shebang line correct to call correct shell but it appears to not be the case??

[mssever]

is there any way to confirm but it looks like the case..

i did a search on yahoo "bash or dash" and found this in http://ubuntuforums.org/archive/index.php/t-221769.html

i thought this means both bash and dash are available in and i need to have the shebang line correct to call correct shell but it appears to not be the case??

If your shebang line calls bash, then I can't imagine what your problem is. Perhaps you could post the current version of your code so I can try it here.

[newsman]

I think bash shebang might be a symbolic link to dash...lol... I don't want to investigate it just now (let the weekend start in UK first)

I submitted the required code. They also said its not working on their servers... They have given me another deadline (three working days). I want to try it myself (cos maybe it is just stupid me) first and that is most productive and beneficial for myself.. I might just focus on this for Friday at least.

Besides. I have another interview and I have been told that they will take a test on Bash and SQL so I will use this weekend to learn more about them. And my C is also much to be desired.

[newsman]

eek I had not completed one requirement...

how can we get real name from login name

id -r login.name is giving me: error:
id: cannnot only print names or real IDs in default format

is there a way to select the second column 1st row output of finger login.name
Because this gives:
Login:login.name Name: Login Name
Directory:don't care Shell: don't care
Rest info: don't care

without using sed or awk

[newsman]

Some how i want this work ...

I got the first part to work, but i want to input into last part to get rid of everything before the last space ( i can check the exact regular expression to use later) but how do i get this to syntactically work....

Another way to do it is input finger -l -p -m $USER | grep Name into a variable.. but i get scriptname: 5: =Login:: not found


~$ finger -l -p -m $USER | grep Name | ${%%" "*}
bash: ${%%" "*}: bad substitution
~$ finger -l -p -m $USER | grep Name | ${$1%%*" "}
bash: ${$1%%*" "}: bad substitution
~$ finger -l -p -m $USER | grep Name | ${$%%*" "}
bash: 15905: command not found
~$

Another idea i had was to use this
finger -l -p -m $USER | grep -o Name:\W
but results in nothing.

if i do finger -l -p -m $USER | grep -o Name:
at least the result is

Name:

[newsman]

After several brainwacking minutes (almost half hour from my edit..oh gosh my concentration) I get:

for:

finger -l -p -m $USER | grep -o Name:" ".*

result:
Name: Login Name

But i would rather get rid of name part but i will submit it early and get some feedback before the deadline...then i can concentrate a bit on sql and bash dash mystery on the weekend

[newsman]

all the work got accepted except one

The following takes a file, finds all occurances of $USER and appends it with that line and line number as follows but

12:user occurance line

But the requirement is that the format should be

12)user occurance line

I accomplished this via vim as use of sed and awk is not allowed.

They have got back to me and said, using vim is just like using sed or awk so we will not accept this. What other direction is there?


#!/bin/bash


if [ $# -eq 0 ]

then echo "please pass a filename as an argument" ;

else
{
if [ -f $1 ]
then
{
grep -n $USER $1 >> $1;
vim +%s/:/\)/g +wq $1;

}
fi;
}
fi;

[mssever]

You could do it in Ruby:

echo "$somevar" | ruby -e 'print gets.gsub(/:/,")")'

[newsman]

yep they have made it difficult.

i think they might say,,, well using ruby is same as using sed or awk or vim hahaha (orginally they never said you cannot use vim but after submission they came back and said, well using vim is same as using sed or awk).

i did

grep -n $USER $1 | ruby -e 'print gets.gsub(/:/,")")' | cat

and only get the first occurance rather than all occurances.

[mssever]

Well, you could run it in a loop. But if you're required to stick to pure bash, read up on parameter expansion, and check out the Advanced Bash Scripting Guide (http://tldp.org/LDP/abs/html/). I don't have any personal experience solving such a problem in pure bash, as I don't see much point in it.

[newsman]

I have edited the file so it comes to variable now, (which works haha) now to edit the variable.

$VAR | grep -n $USER $1 ; echo -n "$VAR";

which gives the output
6:line
10:line
34:line

etc..

is there way to run through a loop sub : with )

how about using this properly?

nl [?bp")"?] $VAR



i got this from someone else but i don't know how to use it for my purpose with creating a temp file.

while read filename
do
grep ?$user? > temp
newform ?p[)] temp
nl [?bp?$user?] [temp]
cat temp
done

Thhe problem is only need
newform ?p[)] temp
nl [?bp?$user?] [temp]

to act on a variable as temp file creation is not allowed for this exercise.

and i am getting Syntax error: ")" unexpected (expecting "done") error on using the two commands and if do put ) in quotes in the first line

So my main code looks like:


#!/bin/bash
if [ $# -eq 0 ]
then echo "please pass a filename as an argument" ;
else
{
if [ -f $1 ]
else
then
{
$VAR | grep $USER $1 ; echo -n "$VAR";
# vim +%s/:/\)/g +wq $1;

while read $VAR
do
newform ?p[")"] $VAR
nl [?bp?] $VAR
done
echo "$VAR"

}
fi
}
fi



the output does not change and i get an additional error as follows:




line
line
line
line
line
read: 27: arg count

[newsman]

Why doesn't this work?

#!/bin/bash


if [ $# -eq 0 ]

then echo "please pass a filename as an argument" ;

else
{
if [ -f $1 ]
then
{
$VAR | grep -n $USER $1 ; echo -n $VAR;

$newVAR=${VAR//\:/\)}
echo $newVAR
}
fi
}
fi

it results in bad substitution error.


taken from your link above Bash advanced scripting guide:

${string//substring/replacement} Replace all matches of $substring with $replacement

[mssever]

Try different escaping. Maybe \) is special. Maybe you need to escape the backslashes. I have no experience in this, so I really can't tell you much. Maybe you could poke ghostdog74 on this.

[ghostdog74]

Why doesn't this work?

#!/bin/bash


if [ $# -eq 0 ]

then echo "please pass a filename as an argument" ;

else
{
if [ -f $1 ]
then
{
$VAR | grep -n $USER $1 ; echo -n $VAR;

$newVAR=${VAR//\:/\)}
echo $newVAR
}
fi
}
fi

it results in bad substitution error.


taken from your link above Bash advanced scripting guide:

${string//substring/replacement} Replace all matches of $substring with $replacement

1) ask your teacher , can grep be used?
2) What is $VAR, and where have you defined it?
3) What exactly is it you want to do, substitute ":" with ")" ?
Bash

# s="d:e"
# echo $s
d:e
# echo ${s/:/)}
d)e

of course, you should be using a bash shell to do this.