JCL Concatenation

Code Example

## JCL Concatenation

Concatenation combines multiple datasets into a single logical file, read sequentially as one.

### Syntax
\`\`\`jcl
//DDNAME   DD DSN=FIRST.DATASET,DISP=SHR
//         DD DSN=SECOND.DATASET,DISP=SHR
//         DD DSN=THIRD.DATASET,DISP=SHR
\`\`\`

### Rules
1. First DD has the ddname
2. Following DDs have no name
3. All must be readable
4. Order matters (searched first to last)

### Common Uses
1. **Library concatenation**: Multiple load libraries
2. **Input files**: Process multiple files as one
3. **Copybooks**: Multiple source libraries

### DCB Considerations
- First dataset's DCB attributes used
- BLKSIZE: Largest in concatenation
- All should have compatible attributes

### Limits
- Maximum 255 datasets in concatenation
- All must be same type (sequential or PDS)

### STEPLIB Example
\`\`\`jcl
//STEPLIB  DD DSN=USER.LOADLIB,DISP=SHR
//         DD DSN=TEST.LOADLIB,DISP=SHR
//         DD DSN=PROD.LOADLIB,DISP=SHR
\`\`\`
Programs found in first library used.