I'm fairly new to the world of writing Bash scripts and am needing some guidance. I've begun writing a script for work, and so far so good. However, I'm now at a part that needs to collect database names. The names are actually stored in a file, and I can grep them.
The command I was given is cat /etc/oratab which produces something like this:
# This file is used by ORACLE utilities. It is created by root.sh
# and updated by the Database Configuration Assistant when creating
# a database.
# A colon, ':', is used as the field terminator. A new line terminates
# the entry. Lines beginning with a pound sign, '#', are comments.
#
# The first and second fields are the system identifier and home
# directory of the database respectively. The third filed indicates
# to the dbstart utility that the database should , "Y", or should not,
# "N", be brought up at system boot time.
#
OEM:/software/oracle/agent/agent12c/core/12.1.0.3.0:N
*:/software/oracle/agent/agent11g:N
dev068:/software/oracle/ora-10.02.00.04.11:Y
dev299:/software/oracle/ora-10.02.00.04.11:Y
xtst036:/software/oracle/ora-10.02.00.04.11:Y
xtst161:/software/oracle/ora-10.02.00.04.11:Y
dev360:/software/oracle/ora-11.02.00.04.02:Y
dev361:/software/oracle/ora-11.02.00.04.02:Y
xtst215:/software/oracle/ora-11.02.00.04.02:Y
xtst216:/software/oracle/ora-11.02.00.04.02:Y
dev298:/software/oracle/ora-11.02.00.04.03:Y
xtst160:/software/oracle/ora-11.02.00.04.03:Y
I turn turned around and wrote grep ":/software/oracle/ora" /etc/oratab so it can grab everything I need, which is 10 databases. Not the most elegant way, but it gets what I need:
dev068:/software/oracle/ora-10.02.00.04.11:Y
dev299:/software/oracle/ora-10.02.00.04.11:Y
xtst036:/software/oracle/ora-10.02.00.04.11:Y
xtst161:/software/oracle/ora-10.02.00.04.11:Y
dev360:/software/oracle/ora-11.02.00.04.02:Y
dev361:/software/oracle/ora-11.02.00.04.02:Y
xtst215:/software/oracle/ora-11.02.00.04.02:Y
xtst216:/software/oracle/ora-11.02.00.04.02:Y
dev298:/software/oracle/ora-11.02.00.04.03:Y
xtst160:/software/oracle/ora-11.02.00.04.03:Y
So, if I want to grab the name, such as dev068 or xtst161, how do I? I think for what I need to do with this project moving forward, is storing them in an array. As mentioned in the documentation, a colon is the field terminator. How could I whip this together so I have an array, something like:
dev068
dev299
xtst036
xtst161
dev360
dev361
xtst215
xtst216
dev298
xtst160
I feel like I may be asking for too much assistance here but I'm truly at a loss. I would be happy to clarify if need be.
It is much simpler using awk:
awk -F: -v key='/software/oracle/ora' '$2 ~ key{print $1}' /etc/oratab
dev068
dev299
xtst036
xtst161
dev360
dev361
xtst215
xtst216
dev298
xtst160
To populate a BASH array with above output use:
mapfile -t arr < <(awk -F: -v key='/software/oracle/ora' '$2 ~ key{print $1}' /etc/oratab)
To check output:
declare -p arr
declare -a arr='([0]="dev068" [1]="dev299" [2]="xtst036" [3]="xtst161" [4]="dev360" [5]="dev361" [6]="xtst215" [7]="xtst216" [8]="dev298" [9]="xtst160")'
We can pipe the output of grep to the cut utility to extract the first field, taking colon as the field separator.
Then, assuming there are no whitespace or glob characters in any of the names (which would be subject to word splitting and filename expansion), we can use a command substitution to run the pipeline, and capture the output in an array by assigning it within the parentheses.
names=($(grep ':/software/oracle/ora' /etc/oratab| cut -d: -f1;));
Note that the above command actually makes use of word splitting on the command substitution output to split the names into separate elements of the resulting array. That is why we must be sure that no whitespace occurs within any single database name, otherwise that name would be internally split into separate elements of the array. The only characters within the command substitution output that we want to be taken as word splitting delimiters are the line feeds that delimit each line of output coming off the cut utility.
You could also use awk for this:
awk -F: '!/^#/ && $2 ~ /^\/software\/oracle\/ora-/ {print $1}' /etc/oratab
The first pattern excludes any commented-out lines (starting with a #). The second pattern looks for your expected directory pattern in the second field. If both conditions are met it prints the first field, which the Oracle SID. The -F: flag sets the field delimiter to a colon.
With your file that gets:
dev068
dev299
xtst036
xtst161
dev360
dev361
xtst215
xtst216
dev298
xtst160
Depending on what you're doing you could finesse it further and check the last flag is set to Y; although that is really to indicate automatic start-up, it can sometime be used to indicate that a database isn't active at all.
And you can put the results into an array with:
declare -a DBS=(`awk -F: -v key='/software/oracle/ora' '$2 ~ key{print $1}' /etc/oratab`)
and then refer to ${DBS[1]} (which evaluates to dev299) etc.
If you'd like them into a Bash array:
$ cat > toarr.bash
#!/bin/bash
while read -r line
do
if [[ $line =~ .*Y$ ]] # they seem to end in a "Y"
then
arr[$((i++))]=${line%%:*}
fi
done < file
echo ${arr[*]} # here we print the array arr
$ bash toarr.bash
dev068 dev299 xtst036 xtst161 dev360 dev361 xtst215 xtst216 dev298 xtst160
Related
I have a file with three columns, which has pipe as a delimiter. Now some lines in the file can have a "," instead of "|", due to some error. I want to output all such erroneous rows.
You can also use grep, it is more complicated:
egrep "\|.*\|.*\|" input
echo No pipe
egrep "^[^\|]*$" input
echo One pipe
egrep "^[^\|]*\|[^\|\]*$" input
echo 3+ pipe
egrep "\|[^\|]*\|[^\|\]*\|" input
Before combining the greps, first introduce new variables
p (pipe) and n (no pipe)
p="\|"
n="[^\|]*"
echo "p=$p, n=$n"
echo No pipe
egrep "^$n$" input
echo One pipe
egrep "^$n$p$n$" input
echo 3+ pipe
egrep "$p$n$p$n$p" input
Now bring all together
egrep "^$n$|^$n$p$n$|$p$n$p$n$p" input
Edit: The comments and variable names were about "slashes", but they are pipes (with backslashes). That was a bit confusing.
To count the number of columns with awk you can use the NF variable:
$ cat file
ABC|12345|EAR
PQRST|123|TWOEYES
ssdf|fdas,sdfsf
$ awk -F\| 'NF!=3' file
ssdf|fdas,sdfsf
However, this does not seem to cover all the possible ways the data could be corrupted based on the various revisions of the question and the comments.
A better approach would be to define the exact format that the data must follow. For example, assuming that a line is "correct" if it is three columns, with the first and third letters only, and the second numeric, you could write the following script to match all non conforming lines:
awk -F\| '!(NF==3 && $1$3 ~ /^[a-zA-Z]+$/ && $2+0==$2)' file
Test (notice that only the second line (which is conforming) does not get printed):
$ cat file
A,BC|12345|EAR
PQRST|123|TWOEYES
ssdf|fdas,sdfsf
ABC|3983|MAKE,
sf dl lfsdklf |kldsamfklmadkfmask |mfkmadskfmdslafmka
ABC|abs|EWE
sdf|123|123
$ awk -F\| '!(NF==3&&$1$3~/^[a-zA-Z]+$/&&$2+0==$2)' file
A,BC|12345|EAR
ssdf|fdas,sdfsf
ABC|3983|MAKE,
sf dl lfsdklf |kldsamfklmadkfmask |mfkmadskfmdslafmka
ABC|abs|EWE
sdf|123|12
You can adapt the above command to your specific needs, based on what you think is a valid input. For example, if you wanted to also restrict the length of each line to 50 characters, you could do
awk -F\| '!(NF==3 && $1$3 ~ /^[a-zA-Z]+$/ && $2+0==$2 && length($0)<50)' file
I'm really new at Bash and scripting in general.
I have to create usernames formed of first letter of first name followed by last name. To do it, I use a provided text file that looks like this:
doe,john
smith,mike
...
I declared the following variables:
fname=$(cut -d, -f2 "file.txt" | cut -c1)
lname=$(cut -d, -f1 "file.txt")
But how do I put the elements together to form the names jdoe and msmith ? I tried the methods I know to concatenate strings and vriables, but nothing works..
I think I found a method using awk that is supposed to work, but is there any other way to "concatenate" the elements of 2 lists?
Thank you
There's a million ways to do it, this is simplest:
$ awk -F, '{print substr($2,1,1) $1}' file
jdoe
msmith
Ed Morton's awk-based answer is simplest (and probably fastest), but since you asked for a different solution:
#!/usr/bin/env bash
while IFS=, read -r last first _; do
username=${first:0:1}${last}
echo "username: $username"
done < file.txt
IFS=, read -r last first _ reads the first 2 ,-separated fields from each input line (_ is a dummy variable that receives the rest of the input line, if any; -r prevents interpretation of \ chars. in the input, which is usually what you want).
username=${first:0:1}${last} concatenates the 1st char. of variable $first's value with variable $last's value, simply by placing the two variable references next to each other.
${first:0:1} - extract 1 character from $first at position 0 - is an example of parameter expansion, specifically: substring expansion
< file.txt is an input redirection that sends file.txt's contents via stdin to the while loop.
This looks a bit too much like homework, so I'll just drop some hints.
To read the lastname and firstname into separate variables for each line of the file, see BashFAQ 1. It should not involve cut.
To grab the first character of a variable, see BashFAQ 100.
I am new to bash programming and I hit a roadblock.
I need to be able to calculate the largest record number within a txt file and store that into a variable within a function.
Here is the text file:
student_records.txt
12345,fName lName,Grade,email
64674,fName lName,Grade,email
86345,fName lName,Grade,email
I need to be able to get the largest record number ($1 or first field) in order for me to increment this unique record and add more records to the file. I seem to not be able to figure this one out.
First, I sort the file by the first field in descending order and then, perform this operation:
largest_record=$(awk-F,'NR==1{print $1}' student_records.txt)
echo $largest_record
This gives me the following error on the console:
awk-F,NR==1{print $1}: command not found
Any ideas? Also, any suggestions on how to accomplish this in the best way?
Thank you in advance.
largest=$(sort -r file|cut -d"," -f1|head -1)
You need spaces, and quotes
awk -F, 'NR==1{print $1}'
The command is awk, you need a space after it so bash parses your command line properly, otherwise it thinks the whole thing is the name of the command, which is what the error messages is telling you.
Learn how to use the man command so you can learn how to invoke other commands:
man awk
This will tell you what the -F option does:
The -F fs option defines the input field separator to be the regular expression fs.
So in your case the field separator is a comma -F,
What follows in quotes is what you want awk to interpret, it says to match a line with the pattern NR==1, NR is special, it is the record number, so you want it to match the first record, following that is the action you want awk to take when that pattern matches, {print $1}, which says to print the first field (comma separated) of the line.
A better way to accomplish this would be to use awk to find the largest record for you rather than sorting it first, this gives you a solution that is linear in the number for records - you just want the max, no need to do extra work of sorting the whole file:
awk -F, 'BEGIN {max = 0} {if ($1>max) max=$1} END {print max}' student_records.txt
For this and other awk "one liners" look here.
I have a command whose output is of the form:
[{"foo1":<some value>,"foo2":<some value>,"foo3":<some value>}]
I want to take the output of this command and just get the value corresponding to foo2
How do I use sed/awk or any other shell utility readily available in a bash script to do this?
Assuming that the values do not contain commas, this sed rune will do it:
sed -n 's/.*"foo2":\([^,]*\),.*/\1/'p
sed -n tells sed not to print lines by default.
The s ("substitute") command uses a regexp group delimited by \( and \) to pick out just the bit you want.
"foo2": provides the context needed to find the right value.
[^,]* means "a character that is not a comma, any number of times". This is your . If values are not delimited by commas, change this (and the comma after the grouping parens) to match correctly.
.* means "any character, any number of times", and it is used to match all the characters before and after the bit you want. Now the regexp will match the entire line.
\1 means the contents of the grouping parentheses. sed will substitute the string that matches the pattern (which is the whole line, because we used .* at the beginning and end) with the contents of the parens, .
Finally, the p on the end means "print the resulting line".
With this awk for example:
$ awk -F[:,] '{print $4}' file
<some value2>
-F[:,] sets possible field separators as : or ,. Then, it is a matter of counting the position in which <some value> of foo2 are. It happens to be the 4th.
With sed:
$ sed 's/.*"foo2":\([^,]*\).*/\1/g' file
<some value2>
.*"foo2":\([^,]*\).* gets the string coming after foo2: and until the comma appears. Then it prints it back with \1.
Your block of data looks like JSON. There is no native JSON parsing in bash, sed or awk, so ALL the answers here will either suggest that you use a different, more appropriate tool, or they will be hackish and might easily fail if your real data looks different from the example you've provided here.
That said, if you are confident that your variable:value blocks and line structure are always in the same format as this example, you may be able to get away with writing your own (very) basic parser that will work for just your use case.
Note that you can't really parse things in sed, it's just not designed for that. If your data always looks the same, a sed solution may be sufficient ... but remember that you are simply pattern matching, not parsing the input data. There are other answers already which cover this.
For very simple matching of the string that appears after the colon after "foo2", as Peter suggested, you could use the following:
$ data='[{"foo1":11,"foo2":222,"foo3":3333}]'
$ echo "$data" | sed -ne 's/.*"foo2":\([^,]*\),.*/\1/p'
As I say, this should in no way be confused with parsing of your JSON. It would work equally well (or badly) with an input string of abcde"foo2":bar,abcde.
In awk, you can make things that are a bit more advanced, but you still have serious limitations when it comes to JSON. For example, if you choose to separate fields with commas, but then you put a comma inside the <some value> in your data, awk doesn't know how to distinguish it from a field separator.
That said, if your JSON is only one level deep (i.e. matches your sample data), the following might work for you:
$ data='[{"foo1":11,"foo2":222,"foo3":3333}]'
$ echo "$data" | awk -F: -vRS=, '{gsub(/[^[:alnum:]]/,"",$1)} $1=="foo2" {print $2}'
This awk script considers commas as record separators and colons as field separators. It does not support any level of depth in your JSON, and depends on alphanumeric variable names. But it should handle JSON split on to multiple lines.
Alternately, if you want to avoid ugly hacks, and perl or python solutions don't work for you, you might want to try out jsawk. With it, you might use something like this:
$ data='[{"foo1":11,"foo2":222,"foo3":3333}]'
$ echo "$data" | jsawk -a 'return this.foo2'
[222]
SEE ALSO: Parsing json with awk/sed in bash to get key value pair
This worked for me. You can Try this one
echo "[{"foo1":<some value>,"foo2":<some value>,"foo3":<some value>}]" | awk -F"[:,]+" '{ if($3=="foo2") { print $4 }}'
Above line awk uses multiple field separators.I have used colon and comma here
Since this looks like JSON, let's parse it like JSON:
perl -MJSON -ne '$json = decode_json($_); print $json->[0]{foo2}, "\n"' <<END
[{"foo1":"some value","foo2":"some, value","foo3":"some value"}]
END
some, value
I am trying to parse a CSV containing potentially 100k+ lines. Here is the criteria I have:
The index of the identifier
The identifier value
I would like to retrieve all lines in the CSV that have the given value in the given index (delimited by commas).
Any ideas, taking in special consideration for performance?
As an alternative to cut- or awk-based one-liners, you could use the specialized csvtool aka ocaml-csv:
$ csvtool -t ',' col "$index" - < csvfile | grep "$value"
According to the docs, it handles escaping, quoting, etc.
See this youtube video: BASH scripting lesson 10 working with CSV files
CSV file:
Bob Brown;Manager;16581;Main
Sally Seaforth;Director;4678;HOME
Bash script:
#!/bin/bash
OLDIFS=$IFS
IFS=";"
while read user job uid location
do
echo -e "$user \
======================\n\
Role :\t $job\n\
ID :\t $uid\n\
SITE :\t $location\n"
done < $1
IFS=$OLDIFS
Output:
Bob Brown ======================
Role : Manager
ID : 16581
SITE : Main
Sally Seaforth ======================
Role : Director
ID : 4678
SITE : HOME
First prototype using plain old grep and cut:
grep "${VALUE}" inputfile.csv | cut -d, -f"${INDEX}"
If that's fast enough and gives the proper output, you're done.
CSV isn't quite that simple. Depending on the limits of the data you have, you might have to worry about quoted values (which may contain commas and newlines) and escaping quotes.
So if your data are restricted enough can get away with simple comma-splitting fine, shell script can do that easily. If, on the other hand, you need to parse CSV ‘properly’, bash would not be my first choice. Instead I'd look at a higher-level scripting language, for example Python with a csv.reader.
In a CSV file, each field is separated by a comma. The problem is, a field itself might have an embedded comma:
Name,Phone
"Woo, John",425-555-1212
You really need a library package that offer robust CSV support instead of relying on using comma as a field separator. I know that scripting languages such as Python has such support. However, I am comfortable with the Tcl scripting language so that is what I use. Here is a simple Tcl script which does what you are asking for:
#!/usr/bin/env tclsh
package require csv
package require Tclx
# Parse the command line parameters
lassign $argv fileName columnNumber expectedValue
# Subtract 1 from columnNumber because Tcl's list index starts with a
# zero instead of a one
incr columnNumber -1
for_file line $fileName {
set columns [csv::split $line]
set columnValue [lindex $columns $columnNumber]
if {$columnValue == $expectedValue} {
puts $line
}
}
Save this script to a file called csv.tcl and invoke it as:
$ tclsh csv.tcl filename indexNumber expectedValue
Explanation
The script reads the CSV file line by line and store the line in the variable $line, then it split each line into a list of columns (variable $columns). Next, it picks out the specified column and assigned it to the $columnValue variable. If there is a match, print out the original line.
Using awk:
export INDEX=2
export VALUE=bar
awk -F, '$'$INDEX' ~ /^'$VALUE'$/ {print}' inputfile.csv
Edit: As per Dennis Williamson's excellent comment, this could be much more cleanly (and safely) written by defining awk variables using the -v switch:
awk -F, -v index=$INDEX -v value=$VALUE '$index == value {print}' inputfile.csv
Jeez...with variables, and everything, awk is almost a real programming language...
For situations where the data does not contain any special characters, the solution suggested by Nate Kohl and ghostdog74 is good.
If the data contains commas or newlines inside the fields, awk may not properly count the field numbers and you'll get incorrect results.
You can still use awk, with some help from a program I wrote called csvquote (available at https://github.com/dbro/csvquote):
csvquote inputfile.csv | awk -F, -v index=$INDEX -v value=$VALUE '$index == value {print}' | csvquote -u
This program finds special characters inside quoted fields, and temporarily replaces them with nonprinting characters which won't confuse awk. Then they get restored after awk is done.
index=1
value=2
awk -F"," -v i=$index -v v=$value '$(i)==v' file
I was looking for an elegant solution that support quoting and wouldn't require installing anything fancy on my VMware vMA appliance. Turns out this simple python script does the trick! (I named the script csv2tsv.py, since it converts CSV into tab-separated values - TSV)
#!/usr/bin/env python
import sys, csv
with sys.stdin as f:
reader = csv.reader(f)
for row in reader:
for col in row:
print col+'\t',
print
Tab-separated values can be split easily with the cut command (no delimiter needs to be specified, tab is the default). Here's a sample usage/output:
> esxcli -h $VI_HOST --formatter=csv network vswitch standard list |csv2tsv.py|cut -f12
Uplinks
vmnic4,vmnic0,
vmnic5,vmnic1,
vmnic6,vmnic2,
In my scripts I'm actually going to parse tsv output line by line and use read or cut to get the fields I need.
Parsing CSV with primitive text-processing tools will fail on many types of CSV input.
xsv is a lovely and fast tool for doing this properly. To search for all records that contain the string "foo" in the third column:
cat file.csv | xsv search -s 3 foo
A sed or awk solution would probably be shorter, but here's one for Perl:
perl -F/,/ -ane 'print if $F[<INDEX>] eq "<VALUE>"`
where <INDEX> is 0-based (0 for first column, 1 for 2nd column, etc.)
Awk (gawk) actually provides extensions, one of which being csv processing.
Assuming that extension is installed, you can use awk to show all lines where a specific csv field matches 123.
Assuming test.csv contains the following:
Name,Phone
"Woo, John",425-555-1212
"James T. Kirk",123
The following will print all lines where the Phone (aka the second field) is equal to 123:
gawk -l csv 'csvsplit($0,a) && a[2] == 123 {print $0}'
The output is:
"James T. Kirk",123
How does it work?
-l csv asks gawk to load the csv extension by looking for it in $AWKLIBPATH;
csvsplit($0, a) splits the current line, and stores each field into a new array named a
&& a[2] == 123 checks that the second field is 123
if both conditions are true, it { print $0 }, aka prints the full line as requested.