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Topics

Introduction to Bash

What is BashBash vs. other shellsInstalling BashBash environment setupBash command structure

Bash Basics

Bash command line interfaceBash shell promptBash basic commandsBash file system navigationBash file manipulationBash input/output redirectionBash pipesBash command historyBash tab completionBash wildcards and globbing

Bash Variables and Data Types

Bash variables declarationBash environment variablesBash variable scopeBash string manipulationBash arraysBash arithmetic operations

Bash Control Structures

Bash if-else statementsBash case statementsBash for loopsBash while loopsBash until loopsBash break and continueBash select statements

Bash Functions

Bash function declarationBash function parametersBash function return valuesBash local variablesBash recursive functions

Bash Input and Output

Bash read commandBash echo commandBash printf commandBash here documentsBash process substitution

Bash File Operations

Bash file testingBash file permissionsBash file comparisonBash file archiving and compression

Bash Text Processing

Bash grep commandBash sed commandBash awk commandBash cut commandBash sort commandBash uniq commandBash regular expressions

Bash Scripting

Bash script structureBash shebangBash script executionBash command line argumentsBash exit statusBash debugging techniquesBash error handling

Bash Advanced Topics

Bash process managementBash job controlBash signal handlingBash trapsBash subshellsBash command substitutionBash parameter expansionBash brace expansionBash tilde expansionBash aliasesBash options and settings

Bash Best Practices

Bash script organizationBash coding styleBash performance optimizationBash security considerationsBash script portability

Bash and System Administration

Bash system monitoringBash user managementBash network operationsBash cron jobsBash log file analysis

Bash Input/Output Redirection

Input/output redirection is a fundamental concept in Bash that allows you to control the flow of data between commands and files. It's an essential skill for efficient shell scripting and command-line operations.

Understanding I/O Streams

Bash uses three standard I/O streams:

  • stdin (0): Standard input
  • stdout (1): Standard output
  • stderr (2): Standard error

Output Redirection

To redirect output to a file, use the > operator:

echo "Hello, World!" > output.txt

This command writes the output to output.txt, overwriting its contents. To append instead, use >>:

echo "Appended line" >> output.txt

Input Redirection

To use a file as input, employ the < operator:

sort < unsorted_list.txt

This command sorts the contents of unsorted_list.txt.

Error Redirection

Redirect error messages using 2>:

ls non_existent_directory 2> error.log

This captures error messages in error.log.

Combining Redirections

You can redirect both output and error streams:

command > output.txt 2> error.log

To send both streams to the same file:

command &> combined_output.log

Here Documents

For multi-line input, use here documents:

cat << EOF > multiline.txt
Line 1
Line 2
Line 3
EOF

This creates a file with three lines of text. Here documents are particularly useful in Bash script structures.

Practical Applications

  • Logging: Redirect output to log files for later analysis
  • Silent execution: Redirect output to /dev/null to suppress it
  • Input automation: Use input redirection to feed commands with prepared data

Best Practices

  • Always consider potential file overwriting when using >
  • Use >> for logs to append rather than overwrite
  • Redirect errors to separate files for easier debugging
  • Combine redirection with Bash pipes for complex data processing

Mastering input/output redirection enhances your ability to manipulate data streams effectively in Bash. It's a crucial skill for both everyday command-line use and advanced Bash scripting.